Spider

Spider

Overview
Spiders are air-breathing arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s that have eight legs, and chelicerae with fangs that inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 with the exception of air and sea colonization.
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Encyclopedia
Spiders are air-breathing arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s that have eight legs, and chelicerae with fangs that inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 with the exception of air and sea colonization. As of 2008, approximately 40,000 spider species, and 109 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 have been recorded by taxonomists
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

; however, there has been confusion within the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

 as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.

Anatomically, spiders differ from other arthropods in that the usual body segments
Segmentation (biology)
Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 are fused into two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

, and joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

. Unlike insects, spiders do not have antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

. In all except the most primitive group, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 from up to six types of silk glands within their abdomen. Spider web
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....

s vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s with silk-producing spigots appear in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period about , but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks from , and are very similar to the most primitive surviving order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

. The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic period, before .

A herbivorous species, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

, was described in 2008, but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lasso
Lasso
A lasso , also referred to as a lariat, riata, or reata , is a loop of rope that is designed to be thrown around a target and tighten when pulled. It is a well-known tool of the American cowboy. The word is also a verb; to lasso is to successfully throw the loop of rope around something...

ing it with sticky bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, and they liquidize their food by flooding it with digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s and grinding it with the bases of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, as they do not have true jaws.

Male spiders identify themselves by a variety of complex courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to avoid being eaten by the females. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the aggressive widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and other mygalomorph
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 spiders can live up to 25 years in captivity.

While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s. Spider silk provides a combination of lightness, strength and elasticity
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....

 that is superior to that of synthetic materials, and spider silk genes have been inserted into mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology
Mythology
The term mythology can refer either to the study of myths, or to a body or collection of myths. As examples, comparative mythology is the study of connections between myths from different cultures, whereas Greek mythology is the body of myths from ancient Greece...

 symbolizing various combinations of patience, cruelty and creative powers.

Body plan




Spiders are chelicerates and therefore arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s. As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 made of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

 and proteins; heads that are composed of several segments that fuse during the development of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. Being chelicerates, their bodies consist of two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, sets of segments that serve similar functions: the foremost one, called the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 or prosoma, is a complete fusion of the segments that in an insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 would form two separate tagmata, the head and thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

; the rear tagma is called the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 or opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...

. In spiders the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

 typical of most arthropods. In fact chelicerates' only appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, and serve different functions within different groups of chelicerates.


Spiders and scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are members of one chelicerate group, the arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fang
Fang
Fang is a mammal's canine tooth.Fang may also refer to:* A snake's poison-injecting tooth: see snake venom* Fang people, in Central Africa* Fang language, spoken by Fang people...

s that are generally venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

ous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition those of male spiders have enlarged last sections used for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 transfer.

In spiders the cephalothorax and abdomen are joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

, which enables the abdomen to move independently when producing silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

. The upper surface of the cephalothorax is covered by a single, convex carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, whose living members are the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, have segmented plates on the upper surface.

Circulation and respiration



Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

s. The blood of many spiders that have book lung
Book lung
A book lung is a type of respiration organ used for atmospheric gas exchange and is found in arachnids, such as scorpions and spiders. Each of these organs is found inside a ventral abdominal cavity and connects with the surroundings through a small opening. Book lungs are not related to the lungs...

s contains the respiratory pigment
Respiratory pigment
A respiratory pigment is a molecule, such as hemoglobin in humans, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, haemocyanin, haemerythrin and chlorocruorin...

 hemocyanin
Hemocyanin
Hemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...

 to make oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 transport more efficient.

Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....

 system, or both. Mygalomorph and Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. This is also the case for some basal araneomorph spiders like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The trachea system has most likely evolved in small ancestors to help resist desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

. The trachea were originally connected to the surroundings through a pair of openings called spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

s, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets. Spiders that have tracheae generally have higher metabolic rates and better water conservation.

Feeding, digestion and excretion



Uniquely among chelicerates, the final sections of spiders' chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 are fangs, and the great majority of spiders can use them to inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

 into prey from venom gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s in the roots of the chelicerae. Like most arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s including scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, while flooding it with enzymes; in these species the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.

The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.

Most spiders convert nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

ous waste products into uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...

, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

l chamber, from which they are expelled through the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 lineages that can live far away from water, for example the tubules of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s and arachnids develop from completely different parts of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. However a few primitive spiders, the sub-order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and infra-order Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

, retain the ancestral arthropod nephridia ("little kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s"), which use large amounts of water to excrete nitrogenous waste products as ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

.

Central nervous system


The basic arthropod central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 consists of a pair of nerve cord
Ventral nerve cord
The ventral nerve cord makes up the nervous system of some phyla of the invertebrates, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral plane of the organism...

s running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

 is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, of which the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

 are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.

Eyes



Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum
Tapetum lucidum
The tapetum lucidum is a layer of tissue in the eye of many vertebrate animals....

, and wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s can be spotted by torch light reflected from the tapeta. On the other hand jumping spiders' secondary eyes have no tapeta. Jumping spiders' visual acuity
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....

 exceeds by a factor of ten that of dragonflies
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

, which have by far the best vision among insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.

Other senses


As with other arthropods, spiders' cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

s would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

 and smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

, often by means of setae. Spiders also have in the joints of their limbs slit sensilla
Slit sensilla
The slit sensilla is a small mechanoreceptory organ in the exoskeleton of spiders which detects strain due to forces experienced by the animal. As the name indicates, a slit sensilla is a small groove in the exoskeleton which deforms under stress, and these deformations are detected by neurons...

e that detect forces and vibrations. In web-building spiders all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.

Like most arthropods, spiders lack balance and acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand little is known about what other internal sensors spiders or other arthropods may have.

Locomotion


Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. As a result a spider with a punctured cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs.

Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s, keep at least four legs on the surface while walking or running.

Silk production



The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

. Each spinneret has many spigots, each of which is connected to one silk gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

. There are at least six types of silk gland, each producing a different type of silk.

Silk is mainly composed of a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 to nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 and biological materials such as chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

, collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 and cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

, but is much more elastic, in other words it can stretch much further before breaking or losing shape.

Some spiders have a cribellum
Cribellum
The cribellum is a silk spinning organ found in certain spiders. Unlike normal spinnerets, the cribellum consists of one or more plates covered in thousands of tiny spigots. These spigots produce extremely fine fibers which are combed out by the spider's calamistrum, producing silk with a wooly...

, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum
Calamistrum
In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are...

, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However most modern groups of spiders have lost the cribellum.

Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 and for fertilized eggs; as a "safety rope
Safety harness
A safety harness is a form of protective equipment designed to protect a person, animal, or object from injury or damage. The harness is an attachment between a stationary and non-stationary object and is usually fabricated from rope, cable or webbing and locking hardware...

"; for nest-building; and as "parachute
Parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

s" by the young of some species.

Reproduction and life cycle


Spiders reproduce sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...

ually and fertilization is internal
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

 but indirect, in other words the sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, male spiders do not produce ready-made spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

s (packages of sperm) but spin small sperm webs on to which they ejaculate and then transfer the sperm to syringe
Syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...

-like structures on the tips of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell".


Spiders generally use elaborate courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, which have excellent eyesight. If courtship is successful, the male injects his sperm from the pedipalps into the female's genital opening, known as the epigyne
Epigyne
The epigyne or epigynum is the external genital structure of female spiders. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species...

, on the underside of her abdomen. Female's reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.

Males of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Tidarren
Tidarren
Tidarren is a genus of spiders. The males are much smaller than females.The males of this genus amputate one of their palps before maturation and enter their adult life with one palp only...

 amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....

i species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male. In over 60% of cases the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.

Females lay up to 3,000 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 in one or more silk egg sacs, which maintain a fairly constant humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

 level. In some species the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 or attaching them to the spinnerets and dragging them along.

Baby spiders pass all their larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

l stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...

 food.

Like other arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, spiders have to molt to grow as their cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s can live in captivity for over 20 years.


Size


Spiders occur in a large range of sizes. The smallest, Patu digua
Patu digua
Patu digua is by some accounts considered to be the smallest spider in the world, with males reaching a body size of about 0.37 mm. Small as the head of a pin. However, there are other spider species of similar size where only the female is known. Because male spiders are usually smaller than...

 from Colombia, are less than 0.37 mm (0.0145669291338583 in) in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm (3.5 in) and leg spans up to 250 mm (10 in).

Coloration


Only three classes of pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 (ommochrome
Ommochrome
Ommochrome refers to several biological pigments that occur in the eyes of crustaceans and insects. The eye color is determined by the ommochromes. Ommochromes are also found in the chromatophores of cephalopods, and in spiders....

s, bilins
Bilin (biochemistry)
Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrins. Bilin was named as a bile pigment of mammals, but can also be found in lower vertebrates, invertebrates, as well as red algae, green plants and cyanobacteria...

 and guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

s, carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...

s and pterin
Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a keto group and an amino group on positions 4 and 2 respectively...

s, very common in other animals, are apparently absent. In some species the exocuticle of the legs and prosoma is modified by a tanning
Tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

 process, resulting in brown coloration.
Bilins are found, for example, in Micrommata virescens
Micrommata virescens
The green huntsman spider is a spider of the family Sparassidae. It does not build a web, and hunts insects in green vegetation, where it is well camouflaged....

, resulting in its green color. Guanine is responsible for the white markings of the European garden spider
European garden spider
The European garden spider, diadem spider, cross spider, or cross orbweaver is a very common and well-known orb-weaver spider in Europe and parts of North America, in a range extending from New England and the Southeast to California and the northwestern United States and adjacent parts of...

 Araneus diadematus. It is in many species accumulated in specialized cells called guanocytes. In genera such as Tetragnatha
Tetragnatha
Tetragnatha is a genus of spiders containing hundreds of species. They are found all over the world, although most occur in the tropics and subtropics. They are commonly called stretch spiders, referring to their elongated body form...

, Leucauge
Leucauge
Leucauge is a spider genus with pantropical distribution.The body and leg shapes and the silver, black and yellow markings of Leucauge females make identification of the genus relatively easy. They have two rows of long, slender curved hairs on the femurs of the fourth leg...

, Argyrodes
Argyrodes
Spiders of the genus Argyrodes , also called dewdrop spiders, occur worldwide. They are best known as kleptoparasites: they steal other spiders' prey. They invade and reside in their host's web even though they can spin their own webs...

 or Theridiosoma, guanine creates their silvery appearance. While guanine is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage. Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of Argiope
Argiope (spider)
The genus Argiope includes rather large and spectacular spiders that have often a strikingly coloured abdomen. These are well distributed throughout the world, and most countries in temperate or warmer climates have one or more species, which look similar....

 results from hairs reflecting the light, Lycosa
Lycosa
Lycosa is a genus of wolf spiders. More than 200 species are found, represented throughout most of the world. Often called the "true tarantula", Lycosa can be distinguished from common wolf spiders by their relatively large size...

 and Josa
Josa
Josa is a municipality located in the province of Teruel, Aragon, Spain. According to the 2004 census , the municipality has a population of 30 inhabitants....

 both have areas of modified cuticle that act as light reflectors.

Non-predatory feeding


Although spiders are generally regarded as predatory, the jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

 Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 gets over 90% of its food from fairly solid plant material produced by acacia
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...

s as part of a mutually beneficial relationship with a species of ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...

.

Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been under-estimated. Nectar contains amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s, vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...

s and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.

Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....

s, marmalade
Marmalade
Marmalade is a fruit preserve made from the juice and peel of citrus fruits, boiled with sugar and water. The benchmark citrus fruit for marmalade production in Britain is the "Seville orange" from Spain, Citrus aurantium var...

, milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 and sausages.

Methods of capturing prey




The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.

Females of the water spider Argyroneta aquatica build underwater "diving bell" webs which they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.

Net-casting spiders weave only small webs but then manipulate them to trap prey. Those of the genus Hyptiotes
Hyptiotes
-Feeding:Hyptiotes creates a triangular web and sits at a vertex until it detects vibrations that signify the collision of its prey. At this moment hyptiotes releases a coil of silk which it has held taught in such a manner that the tension of the web causes it to entangle the spider's prey. The...

 and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae
Deinopidae
The spider family Deinopidae consists of stick-like elongate spiders that build unusual webs that they suspend between the front legs. When prey approaches, the spider will stretch the net to two or three times its relaxed size and propel itself onto the prey, entangling it in the web...

 weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis
Deinopis
Deinopis is a genus of net-casting spiders.-Name:The genus name is derived from the Greek deinos "fearful" and opis "appearance"; see also the family name "ogre-faced" spiders.-Species:...

 spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa
Deinopis subrufa
Deinopis subrufa is a species of net-casting spiders. It occurs in eastern Australia and Tasmania. It is a nocturnal hunter, having excellent eyesight, and hunts using a silken net to capture its prey. They feed on a variety of insects - ants, beetles, crickets and other spiders...

 appears to live mainly on tipulid flies that they catch with the backwards strike.

Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

 made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...

s of moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.


The primitive Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, the "trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s" (family Ctenizidae) and many tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s are ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...

s that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...

s, which see ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, fishing spiders and some crab spider
Crab spider
Crab spider is a common name applied loosely to many species of spiders, but most nearly consistently to members of the family Thomisidae...

s capture prey by chasing it, and rely mainly on vision to locate prey.


Some jumping spiders of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that Portias instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators.


Ant-mimicking
Ant mimicry
Ant mimicry is mimicry of ants by other organisms. Ants are abundant all over the world, and insect predators that rely on vision to identify their prey such as birds and wasps normally avoid them, either because they are unpalatable, or aggressive. Thus some other arthropods mimic ants to escape...

 spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in form to their heads to mimic antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna
Synemosyna
Synemosyna is a genus of ant-like jumping spiders that occurs from Argentina to the northern United States.-Species:* Synemosyna americana — Mexico to Venezuela* Synemosyna ankeli Cutler & Müller, 1991 — Colombia...

 walk on the outer edges of leaves in the same way as Pseudomyrmex
Pseudomyrmex
Pseudomyrmex is a genus of stinging, wasp-like ants in the family Formicidae . They are large eyed, slender ants with an arboreal habitat. They are found exclusively in the New World in tropical and subtropical regions...

. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

", such as aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...

s. When at rest, the ant-mimicking crab spider Amyciaea
Amyciaea
Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey .-Species:* Amyciaea albomaculata * Amyciaea forticeps Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey...

 does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.

Defense


There is strong evidence that spiders' coloration is camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...

 that helps them to evade their major predators, birds and parasitic wasp
Parasitic wasp
The term parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. They are primarily parasitoids of other animals, mostly other arthropods...

s, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator
Theridion grallator
Theridion grallator, also known as the "happy face spider," is a member of the Theridiidae family.The Hawaiian name is nananana makakii...

, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...

 to offer much benefit. However a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.

Many of the family Theraphosidae, which includes tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and baboon spiders, have urticating hair
Urticating hair
Urticating hairs, i.e. stinging hairs, are one of the primary defense mechanisms used by numerous plants, some New World tarantulas, and various lepidopteran caterpillars. Urtica is Latin for "nettle", and hairs that urticate are characteristic of this type of plant, and many other plants in...

s on their abdomens and use their legs to flick them at attackers. These hairs are fine seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, Carparachne aureoflava
Wheel spider
The Wheel spider, Golden Wheel spider, or Dancing White lady spider , is a huntsman spider native to the Namib Desert of Southern Africa...

, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling
Cartwheel (gymnastics)
In gymnastics, a cartwheel is a sideways rotary movement performed by bringing the hands to the ground while the body inverts and the legs travel over the body, coming down to a standing position.-Terminology:...

 down sand dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...

s.

Social spiders



A few species of spiders that build webs live together in large colonies and show social behavior, although not as complex as in social insects
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....

. Anelosimus
Anelosimus
Anelosimus is a genus of tangle web spider described by Eugène Simon, in 1891, from Venezuela. It includes the South American social spider Anelosimus eximius and related species....

 eximius
Anelosimus eximius
Anelosimus eximius is species of social spider in the genus Anelosimus, native to the Lesser Antilles and the area from Panama to Argentina. Colonies can comprise several thousand individuals....

 (in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

) can form colonies of up to 50,000 individuals. The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

 are at least somewhat social. Members of other species in the same family but several different genera have independently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 developed social behavior. For example, although Theridion
Theridion
The spider genus Theridion, after which the family Theridiidae is named, consists of almost 600 described species that occur all around the world....

 nigroannulatum belongs to a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several Philoponella
Philoponella
Philoponella is a genus of uloborid spiders. Like all Uloboridae, these species have no venom.The species P. vicinus uses its silk to crush its victims to death.-Cooperation:...

 species (family Uloboridae), Agelena consociata
Agelena consociata
Agelena consociata is a social species of funnel web spider that occurs in tropical forests in West Africa and lives in colonies of one to several hundred individuals.-Distribution:This species is found in rainforest habitats in Gabon...

 (family Agelenidae) and Mallos
Mallos (spider)
Mallos is a spider genus belonging to the Dictynidae family.Among the genus, Mallos gregalis is known to be a social spider species, living in groups and signaling each others by vibrating their web.-External links:*...

 gregalis
Mallos gregalis
Mallos gregalis is a spider species belonging to the Dictynidae family.It is known to be a social spider species, living in groups and signaling each others by vibrating their web....

 (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 lives in small colonies which help to protect eggs and spiderlings. Even widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s (genus Latrodectus), which are notoriously aggressive and cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.

Web types


There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 in web construction, in other words use of similar techniques by remotely related species, is rampant. Non-orb web designs and the spinning behaviors that produce them have received very little attention from arachnologists, despite the fact that the majority of spiders build non-orb webs. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasp
Wasp
The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...

s, which are often the dominant predators on spiders, much prefer to attack spiders that have flat webs.

Orb webs



About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection); absorbing its momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 without breaking (stopping); and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.

The hubs of orb webs, where the spiders lurk, are usually above the center as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.

Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as: reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

s to catch insects in slow horizontal flight. However there is no single explanation for the common use of horizontal orb webs.

Spiders often attach highly visible silk bands called decorations or stabilimenta to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.

There are several unusual variants of orb web, many of them convergently evolved, including: attachment of lines to the surface of water, possibly to trap insects in or on the surface; webs with twigs through their centers, possibly to hide the spiders from predators; "ladder-like" webs that appear most effective in catching moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s. However the significance of many variations is unclear.

In 1973, Skylab 3
Skylab 3
Skylab 3 was the second manned mission to Skylab. The Skylab 3 mission started July 28, 1973, with the launch of three astronauts on the Saturn IB rocket, and lasted 59 days, 11 hours and 9 minutes...

 took two orb-web spiders into space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

 to test their web-spinning capabilities in zero gravity. At first both produced rather sloppy webs, but they adapted quickly.

Tangleweb / cobweb spiders



Members of the family Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

 weave irregular, tangled, three-dimensional webs, popularly known as cobwebs.There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.

Other types of webs


The Linyphiidae
Linyphiidae
Linyphiidae is a family of spiders, including more than 4,300 described species in 578 genera worldwide. This makes Linyphiidae the second largest family of spiders after the Salticidae. New species are still being discovered throughout the world, and the family is poorly known...

 generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall on to the sheet or are shaken on to it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.

Fossil record



Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...

. The oldest known amber that contains fossil arthropods dates from in the Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....

n, places where conditions were exceptionally suited to preserving fairly soft tissues.


The oldest known arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

 is the trigonotarbid Palaeotarbus jerami, from about in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 period, and had a triangular cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and segmented abdomen, as well as eight legs and a pair of pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. Attercopus
Attercopus
Previously interpreted as the world's oldest spider, Attercopus fimbriunguis belongs to an extinct order of arachnids named Uraraneida; thought to be close to the origins of spiders...

 fimbriunguis, from in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider. However these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica
Nephila jurassica
Nephila jurassica is an extinct species of spider in the family Nephilidae, which contains the golden silk orb-weavers. The species is known only from the Middle Jurassic Jiulongshan Formation, part of the Daohugou Beds, near the village of Daohugou in Ningcheng County, northeastern China.-History...

, from about , recorded from Daohuogo, Inner Mongolia
Inner Mongolia
Inner Mongolia is an autonomous region of the People's Republic of China, located in the northern region of the country. Inner Mongolia shares an international border with the countries of Mongolia and the Russian Federation...

 in China.

Several Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 spiders were members of the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, a primitive group now represented only by the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

.
The mesothelid Paleothele montceauensis, from the Late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 over , had five spinnerets. Although the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period saw rapid diversification
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...

 of flying insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, there are very few fossil spiders from this period.

The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 well before . Some Triassic mygalomorphs appear to be members of the family Hexathelidae
Hexathelidae
The spider family Hexathelidae, the only family in the super-family Hexatheloidea, is one of two families of spiders known as funnel-webs...

, whose modern members include the notorious Sydney funnel-web spider
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

 account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 periods provide a large number of fossil spiders, including representatives of many modern families.

Family tree



It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms which form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 on the right is based on J.W. Shultz' analysis (2007). Other views include proposals that: scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are more closely related to the extinct marine scorpion-like eurypterid
Eurypterid
Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...

s than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.

Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 feeding system. Instead they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s that are specially adapted for sperm transfer.

Taxonomy


Spiders are divided into two sub-orders, Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and Opisthothelae
Opisthothelae
Opisthothelae is a taxon within Order Araneae, consisting of the Mygalomorphae and the Araneomorphae, but excluding the Mesothelae. Opisthothelae is sometimes presented as an unranked clade and sometimes as a suborder of the Araneae...

, of which the latter contains two infra-orders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

. Over 40,000 living species of spiders (order Araneae) have been identified and are currently grouped into about 110 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 and about 3,700 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 by arachnologists
Arachnology
Arachnology is the scientific study of spiders and related animals such as scorpions, pseudoscorpions, harvestmen, collectively called arachnids. However, the study of ticks and mites is sometimes not included in arachnology, but is called Acarology...

.
  Spider diversity Features
Sub-order Species Genera Families Segmented plates on top of abdomen Ganglia in abdomen Spinnerets Striking direction of fangs
Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

87 5 1 Yes Yes Four pairs, in some species one pair fused, under middle of abdomen Downwards and forwards
Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

2,600 300 15 No, but yes in some fossils No One, two or three pairs under rear of abdomen
Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

37,000 3,400 93 From sides to center, like pincers

Mesothelae




The only living members of the primitive Mesothelae are the family Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, found only in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. Most of the Liphistiidae construct silk-lined burrows with thin trapdoor
Trapdoor
A trapdoor is a door set into a floor or ceiling .Originally, trapdoors were sack traps in mills, and allowed the sacks to pass up through the mill while naturally falling back to a closed position....

s, although some species of the genus Liphistius
Liphistius
Liphistius is a genus of basal trapdoor spiders in the family Liphistiidae. They are found in Japan, China, and Southeast Asia.-Biology:...

 build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus Liphistius run silk "tripwire
Tripwire
A tripwire is a passive triggering mechanism. Typically, a wire or cord is attached to some device for detecting or reacting to physical movement...

s" outwards from their tunnels to help them detect approaching prey, while those of genus Heptathela
Heptathela
Heptathela is a genus of spiders that includes the Kimura-gumo. They are basal trapdoor spiders of the family Liphistiidae and are found in Japan, China, and Southeast Asia.Females are up to 25 mm long, males slightly smaller...

 do not and instead rely on their built-in vibration sensors. Spiders of the genus Heptathela have no venom glands although they do have venom gland outlets on the fang tip.

The extinct families Arthrolycosidae
Arthrolycosidae
Arthrolycosidae is an extinct family of primitive spiders that bear some resemblance to the wolf spiders....

, found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 rocks, and Arthromygalidae
Arthromygalidae
The Arthromygalidae are an extinct family of primitive spiders that bear some resemblance to the tarantulas, at its peak in the Carboniferous, some 280 million years ago....

, so far found only in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks, have been classified as members of the Mesothelae.

Mygalomorphae




The Mygalomorphae, which first appeared in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 period, are generally heavily built and hairy, with large, robust chelicerae and fangs. Well-known examples include tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s, trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s and the Australasian funnel-web spider
Australasian funnel-web spider
Australian funnel-web spiders are venomous spiders of the family Hexathelidae, represented by 31 described species of Hadronyche, four Bymainiella spp., two Teranodes and monotyptic genera Plesiothera fentoni and Ilawarra whisharti...

s. Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "balloon" by using air currents for transport, their populations often form clumps. In addition to arthropods, mygalomorphs prey on frogs and lizards, and snails.

Araneomorphae




In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the "true spiders", include orb-web spiders, the cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...

 wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, and jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, as well as the only known herbivorous spider, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment.

Spider bites


Most spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting. Most of those with medically serious bites, such as recluse spider
Recluse spider
The recluse spiders or brown spiders , also known as fiddle-back, violin spiders or reapers, are a venomous genus of spiders known for their necrotic bite, which sometimes produces a characteristic set of symptoms known as Loxoscelism...

s and widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s, are shy and bite only when they feel threatened, although this can easily arise by accident. Funnel web spiders
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

' defensive tactics are aggressive and their venom, although they rarely inject much, has resulted in 13 known human deaths. On the other hand, the Brazilian wandering spider
Brazilian wandering spider
Phoneutria, commonly known as Brazilian wandering spiders, armed spiders , or banana spiders , are a genus of aggressive and highly venomous spiders found in tropical South and Central America...

 requires very little provocation.

There were about 100 reliably reported deaths from spider bites in the 20th century, but about 1,500 from jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

 stings. Many alleged cases of spider bites may represent incorrect diagnoses, which would make it more difficult to check the effectiveness of treatments for genuine bites.

Benefits to humans


Cooked tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

 spiders are considered a delicacy in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...

, and by the Piaroa
Piaroa
The Piaroa are an indigenous American ethnic group living along the banks of the Orinoco River and its tributaries in present day Venezuela, and in a few scattered locations elsewhere in Venezuela and in Colombia...

 Indians of southern Venezuela – provided the highly irritant hairs, the spiders' main defense system, are removed first.

Spider venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

s may be a less polluting alternative to conventional pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s as they are deadly to insects but the great majority are harmless to vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s. Australian funnel web spiders are a promising source as most of the world's insect pests have had no opportunity to develop any immunity
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...

 to their venom, and funnel web spiders thrive in captivity and are easy to "milk". It may be possible to target specific pests by engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

 genes for the production of spider toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s into virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es that infect species such as cotton bollworm
Cotton bollworm
Cotton bollworm may refer to:* Helicoverpa zea* Helicoverpa armigera, the American bollworm or tomato grub- See also :* Bollworm...

s.

Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

, stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

s, and erectile dysfunction
Erectile dysfunction
Erectile dysfunction is sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual performance....

.

Because spider silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 is both light and very strong, attempts
BioSteel
BioSteel is a trademark name for a high-strength based fiber material made of the recombinant spider silk-like protein extracted from the milk of transgenic goats, made by Nexia Biotechnologies....

 are being made to produce it in goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s' milk and in the leaves of plants, by means of genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

. Fine transparent spider silk fibers are used by physicists, working on optical communications, to introduce minute diffraction patterns over propagating N-slit interferometric signals
N-Slit interferometer
The N-slit interferometer is an extension of the double-slit interferometer also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton...

.

Arachnophobia


Arachnophobia
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

 is a specific phobia
Specific phobia
A specific phobia is a generic term for any kind of anxiety disorder that amounts to an unreasonable or irrational fear related to exposure to specific objects or situations...

, an abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It is one of the most common specific phobias, and some statistics show that 50% of women and 10% of men show symptoms.

It may be an exaggerated form of an instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...

ive response that helped early humans to survive, or perhaps a cultural phenomenon that is most common in predominantly European societies.

Spiders in symbolism and culture


Spiders have been the focus of fears
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

, stories and mythologies of various cultures for centuries. They have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice for the painful death their venom causes.

Web-spinning also caused the association of the spider with creation myths as they seem to have the ability to produce their own worlds. The Moche
Moche
'The Moche civilization flourished in northern Peru from about 100 AD to 800 AD, during the Regional Development Epoch. While this issue is the subject of some debate, many scholars contend that the Moche were not politically organized as a monolithic empire or state...

 people of ancient Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

 worshipped nature. They placed emphasis on animals and often depicted spiders in their art.

See also


  • Endangered spiders
    Endangered spiders
    An endangered species is “a species at risk of extinction because of human activity, changes in climate, changes in predator-prey ratios, etc., especially when officially designated as such by a governmental agency such as the U.S. Fish and Wildlife Service”...

  • Identifying spiders
    Spider taxonomy
    Spider taxonomy is the alpha taxonomy of the spiders, members of the Araneae order of the arthropod class Arachnida with about 40,000 described species. However there are likely many species that have escaped the human eye to this day, and many specimens stored in collections waiting to be...

  • Spider diversity
  • Arachnidism
    Arachnidism
    Arachnidism is a medical condition, simply defined as envenomation by a spider bite, which, depending on the species, will have various effects. Bites from the widow spiders produce a condition known as Latrodectism, while bites from the recluse spiders cause Loxoscelism...

  • Toxins

Footnotes


Spiders (order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Araneae) are air-breathing arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s that have eight legs, and chelicerae with fangs that inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 with the exception of air and sea colonization. As of 2008, approximately 40,000 spider species, and 109 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 have been recorded by taxonomists
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

; however, there has been confusion within the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

 as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.

Anatomically, spiders differ from other arthropods in that the usual body segments
Segmentation (biology)
Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 are fused into two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

, and joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

. Unlike insects, spiders do not have antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

. In all except the most primitive group, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 from up to six types of silk glands within their abdomen. Spider web
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....

s vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s with silk-producing spigots appear in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period about , but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks from , and are very similar to the most primitive surviving order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

. The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic period, before .

A herbivorous species, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

, was described in 2008, but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lasso
Lasso
A lasso , also referred to as a lariat, riata, or reata , is a loop of rope that is designed to be thrown around a target and tighten when pulled. It is a well-known tool of the American cowboy. The word is also a verb; to lasso is to successfully throw the loop of rope around something...

ing it with sticky bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, and they liquidize their food by flooding it with digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s and grinding it with the bases of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, as they do not have true jaws.

Male spiders identify themselves by a variety of complex courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to avoid being eaten by the females. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the aggressive widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and other mygalomorph
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 spiders can live up to 25 years in captivity.

While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s. Spider silk provides a combination of lightness, strength and elasticity
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....

 that is superior to that of synthetic materials, and spider silk genes have been inserted into mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology
Mythology
The term mythology can refer either to the study of myths, or to a body or collection of myths. As examples, comparative mythology is the study of connections between myths from different cultures, whereas Greek mythology is the body of myths from ancient Greece...

 symbolizing various combinations of patience, cruelty and creative powers.

Body plan




Spiders are chelicerates and therefore arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s. As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 made of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

 and proteins; heads that are composed of several segments that fuse during the development of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. Being chelicerates, their bodies consist of two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, sets of segments that serve similar functions: the foremost one, called the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 or prosoma, is a complete fusion of the segments that in an insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 would form two separate tagmata, the head and thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

; the rear tagma is called the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 or opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...

. In spiders the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

 typical of most arthropods. In fact chelicerates' only appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, and serve different functions within different groups of chelicerates.


Spiders and scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are members of one chelicerate group, the arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fang
Fang
Fang is a mammal's canine tooth.Fang may also refer to:* A snake's poison-injecting tooth: see snake venom* Fang people, in Central Africa* Fang language, spoken by Fang people...

s that are generally venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

ous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition those of male spiders have enlarged last sections used for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 transfer.

In spiders the cephalothorax and abdomen are joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

, which enables the abdomen to move independently when producing silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

. The upper surface of the cephalothorax is covered by a single, convex carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, whose living members are the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, have segmented plates on the upper surface.

Circulation and respiration



Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

s. The blood of many spiders that have book lung
Book lung
A book lung is a type of respiration organ used for atmospheric gas exchange and is found in arachnids, such as scorpions and spiders. Each of these organs is found inside a ventral abdominal cavity and connects with the surroundings through a small opening. Book lungs are not related to the lungs...

s contains the respiratory pigment
Respiratory pigment
A respiratory pigment is a molecule, such as hemoglobin in humans, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, haemocyanin, haemerythrin and chlorocruorin...

 hemocyanin
Hemocyanin
Hemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...

 to make oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 transport more efficient.

Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....

 system, or both. Mygalomorph and Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. This is also the case for some basal araneomorph spiders like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The trachea system has most likely evolved in small ancestors to help resist desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

. The trachea were originally connected to the surroundings through a pair of openings called spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

s, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets. Spiders that have tracheae generally have higher metabolic rates and better water conservation.

Feeding, digestion and excretion



Uniquely among chelicerates, the final sections of spiders' chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 are fangs, and the great majority of spiders can use them to inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

 into prey from venom gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s in the roots of the chelicerae. Like most arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s including scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, while flooding it with enzymes; in these species the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.

The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.

Most spiders convert nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

ous waste products into uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...

, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

l chamber, from which they are expelled through the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 lineages that can live far away from water, for example the tubules of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s and arachnids develop from completely different parts of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. However a few primitive spiders, the sub-order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and infra-order Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

, retain the ancestral arthropod nephridia ("little kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s"), which use large amounts of water to excrete nitrogenous waste products as ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

.

Central nervous system


The basic arthropod central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 consists of a pair of nerve cord
Ventral nerve cord
The ventral nerve cord makes up the nervous system of some phyla of the invertebrates, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral plane of the organism...

s running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

 is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, of which the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

 are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.

Eyes



Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum
Tapetum lucidum
The tapetum lucidum is a layer of tissue in the eye of many vertebrate animals....

, and wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s can be spotted by torch light reflected from the tapeta. On the other hand jumping spiders' secondary eyes have no tapeta. Jumping spiders' visual acuity
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....

 exceeds by a factor of ten that of dragonflies
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

, which have by far the best vision among insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.

Other senses


As with other arthropods, spiders' cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

s would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

 and smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

, often by means of setae. Spiders also have in the joints of their limbs slit sensilla
Slit sensilla
The slit sensilla is a small mechanoreceptory organ in the exoskeleton of spiders which detects strain due to forces experienced by the animal. As the name indicates, a slit sensilla is a small groove in the exoskeleton which deforms under stress, and these deformations are detected by neurons...

e that detect forces and vibrations. In web-building spiders all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.

Like most arthropods, spiders lack balance and acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand little is known about what other internal sensors spiders or other arthropods may have.

Locomotion


Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. As a result a spider with a punctured cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs.

Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s, keep at least four legs on the surface while walking or running.

Silk production



The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

. Each spinneret has many spigots, each of which is connected to one silk gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

. There are at least six types of silk gland, each producing a different type of silk.

Silk is mainly composed of a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 to nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 and biological materials such as chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

, collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 and cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

, but is much more elastic, in other words it can stretch much further before breaking or losing shape.

Some spiders have a cribellum
Cribellum
The cribellum is a silk spinning organ found in certain spiders. Unlike normal spinnerets, the cribellum consists of one or more plates covered in thousands of tiny spigots. These spigots produce extremely fine fibers which are combed out by the spider's calamistrum, producing silk with a wooly...

, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum
Calamistrum
In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are...

, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However most modern groups of spiders have lost the cribellum.

Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 and for fertilized eggs; as a "safety rope
Safety harness
A safety harness is a form of protective equipment designed to protect a person, animal, or object from injury or damage. The harness is an attachment between a stationary and non-stationary object and is usually fabricated from rope, cable or webbing and locking hardware...

"; for nest-building; and as "parachute
Parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

s" by the young of some species.

Reproduction and life cycle


Spiders reproduce sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...

ually and fertilization is internal
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

 but indirect, in other words the sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, male spiders do not produce ready-made spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

s (packages of sperm) but spin small sperm webs on to which they ejaculate and then transfer the sperm to syringe
Syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...

-like structures on the tips of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell".


Spiders generally use elaborate courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, which have excellent eyesight. If courtship is successful, the male injects his sperm from the pedipalps into the female's genital opening, known as the epigyne
Epigyne
The epigyne or epigynum is the external genital structure of female spiders. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species...

, on the underside of her abdomen. Female's reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.

Males of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Tidarren
Tidarren
Tidarren is a genus of spiders. The males are much smaller than females.The males of this genus amputate one of their palps before maturation and enter their adult life with one palp only...

 amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....

i species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male. In over 60% of cases the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.

Females lay up to 3,000 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 in one or more silk egg sacs, which maintain a fairly constant humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

 level. In some species the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 or attaching them to the spinnerets and dragging them along.

Baby spiders pass all their larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

l stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...

 food.

Like other arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, spiders have to molt to grow as their cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s can live in captivity for over 20 years.


Size


Spiders occur in a large range of sizes. The smallest, Patu digua
Patu digua
Patu digua is by some accounts considered to be the smallest spider in the world, with males reaching a body size of about 0.37 mm. Small as the head of a pin. However, there are other spider species of similar size where only the female is known. Because male spiders are usually smaller than...

 from Colombia, are less than 0.37 mm (0.0145669291338583 in) in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm (3.5 in) and leg spans up to 250 mm (10 in).

Coloration


Only three classes of pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 (ommochrome
Ommochrome
Ommochrome refers to several biological pigments that occur in the eyes of crustaceans and insects. The eye color is determined by the ommochromes. Ommochromes are also found in the chromatophores of cephalopods, and in spiders....

s, bilins
Bilin (biochemistry)
Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrins. Bilin was named as a bile pigment of mammals, but can also be found in lower vertebrates, invertebrates, as well as red algae, green plants and cyanobacteria...

 and guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

s, carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...

s and pterin
Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a keto group and an amino group on positions 4 and 2 respectively...

s, very common in other animals, are apparently absent. In some species the exocuticle of the legs and prosoma is modified by a tanning
Tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

 process, resulting in brown coloration.
Bilins are found, for example, in Micrommata virescens
Micrommata virescens
The green huntsman spider is a spider of the family Sparassidae. It does not build a web, and hunts insects in green vegetation, where it is well camouflaged....

, resulting in its green color. Guanine is responsible for the white markings of the European garden spider
European garden spider
The European garden spider, diadem spider, cross spider, or cross orbweaver is a very common and well-known orb-weaver spider in Europe and parts of North America, in a range extending from New England and the Southeast to California and the northwestern United States and adjacent parts of...

 Araneus diadematus. It is in many species accumulated in specialized cells called guanocytes. In genera such as Tetragnatha
Tetragnatha
Tetragnatha is a genus of spiders containing hundreds of species. They are found all over the world, although most occur in the tropics and subtropics. They are commonly called stretch spiders, referring to their elongated body form...

, Leucauge
Leucauge
Leucauge is a spider genus with pantropical distribution.The body and leg shapes and the silver, black and yellow markings of Leucauge females make identification of the genus relatively easy. They have two rows of long, slender curved hairs on the femurs of the fourth leg...

, Argyrodes
Argyrodes
Spiders of the genus Argyrodes , also called dewdrop spiders, occur worldwide. They are best known as kleptoparasites: they steal other spiders' prey. They invade and reside in their host's web even though they can spin their own webs...

 or Theridiosoma, guanine creates their silvery appearance. While guanine is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage. Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of Argiope
Argiope (spider)
The genus Argiope includes rather large and spectacular spiders that have often a strikingly coloured abdomen. These are well distributed throughout the world, and most countries in temperate or warmer climates have one or more species, which look similar....

 results from hairs reflecting the light, Lycosa
Lycosa
Lycosa is a genus of wolf spiders. More than 200 species are found, represented throughout most of the world. Often called the "true tarantula", Lycosa can be distinguished from common wolf spiders by their relatively large size...

 and Josa
Josa
Josa is a municipality located in the province of Teruel, Aragon, Spain. According to the 2004 census , the municipality has a population of 30 inhabitants....

 both have areas of modified cuticle that act as light reflectors.

Non-predatory feeding


Although spiders are generally regarded as predatory, the jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

 Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 gets over 90% of its food from fairly solid plant material produced by acacia
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...

s as part of a mutually beneficial relationship with a species of ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...

.

Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been under-estimated. Nectar contains amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s, vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...

s and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.

Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....

s, marmalade
Marmalade
Marmalade is a fruit preserve made from the juice and peel of citrus fruits, boiled with sugar and water. The benchmark citrus fruit for marmalade production in Britain is the "Seville orange" from Spain, Citrus aurantium var...

, milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 and sausages.

Methods of capturing prey




The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.

Females of the water spider Argyroneta aquatica build underwater "diving bell" webs which they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.

Net-casting spiders weave only small webs but then manipulate them to trap prey. Those of the genus Hyptiotes
Hyptiotes
-Feeding:Hyptiotes creates a triangular web and sits at a vertex until it detects vibrations that signify the collision of its prey. At this moment hyptiotes releases a coil of silk which it has held taught in such a manner that the tension of the web causes it to entangle the spider's prey. The...

 and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae
Deinopidae
The spider family Deinopidae consists of stick-like elongate spiders that build unusual webs that they suspend between the front legs. When prey approaches, the spider will stretch the net to two or three times its relaxed size and propel itself onto the prey, entangling it in the web...

 weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis
Deinopis
Deinopis is a genus of net-casting spiders.-Name:The genus name is derived from the Greek deinos "fearful" and opis "appearance"; see also the family name "ogre-faced" spiders.-Species:...

 spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa
Deinopis subrufa
Deinopis subrufa is a species of net-casting spiders. It occurs in eastern Australia and Tasmania. It is a nocturnal hunter, having excellent eyesight, and hunts using a silken net to capture its prey. They feed on a variety of insects - ants, beetles, crickets and other spiders...

 appears to live mainly on tipulid flies that they catch with the backwards strike.

Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

 made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...

s of moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.


The primitive Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, the "trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s" (family Ctenizidae) and many tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s are ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...

s that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...

s, which see ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, fishing spiders and some crab spider
Crab spider
Crab spider is a common name applied loosely to many species of spiders, but most nearly consistently to members of the family Thomisidae...

s capture prey by chasing it, and rely mainly on vision to locate prey.


Some jumping spiders of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that Portias instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators.


Ant-mimicking
Ant mimicry
Ant mimicry is mimicry of ants by other organisms. Ants are abundant all over the world, and insect predators that rely on vision to identify their prey such as birds and wasps normally avoid them, either because they are unpalatable, or aggressive. Thus some other arthropods mimic ants to escape...

 spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in form to their heads to mimic antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna
Synemosyna
Synemosyna is a genus of ant-like jumping spiders that occurs from Argentina to the northern United States.-Species:* Synemosyna americana — Mexico to Venezuela* Synemosyna ankeli Cutler & Müller, 1991 — Colombia...

 walk on the outer edges of leaves in the same way as Pseudomyrmex
Pseudomyrmex
Pseudomyrmex is a genus of stinging, wasp-like ants in the family Formicidae . They are large eyed, slender ants with an arboreal habitat. They are found exclusively in the New World in tropical and subtropical regions...

. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

", such as aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...

s. When at rest, the ant-mimicking crab spider Amyciaea
Amyciaea
Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey .-Species:* Amyciaea albomaculata * Amyciaea forticeps Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey...

 does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.

Defense


There is strong evidence that spiders' coloration is camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...

 that helps them to evade their major predators, birds and parasitic wasp
Parasitic wasp
The term parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. They are primarily parasitoids of other animals, mostly other arthropods...

s, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator
Theridion grallator
Theridion grallator, also known as the "happy face spider," is a member of the Theridiidae family.The Hawaiian name is nananana makakii...

, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...

 to offer much benefit. However a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.

Many of the family Theraphosidae, which includes tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and baboon spiders, have urticating hair
Urticating hair
Urticating hairs, i.e. stinging hairs, are one of the primary defense mechanisms used by numerous plants, some New World tarantulas, and various lepidopteran caterpillars. Urtica is Latin for "nettle", and hairs that urticate are characteristic of this type of plant, and many other plants in...

s on their abdomens and use their legs to flick them at attackers. These hairs are fine seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, Carparachne aureoflava
Wheel spider
The Wheel spider, Golden Wheel spider, or Dancing White lady spider , is a huntsman spider native to the Namib Desert of Southern Africa...

, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling
Cartwheel (gymnastics)
In gymnastics, a cartwheel is a sideways rotary movement performed by bringing the hands to the ground while the body inverts and the legs travel over the body, coming down to a standing position.-Terminology:...

 down sand dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...

s.

Social spiders



A few species of spiders that build webs live together in large colonies and show social behavior, although not as complex as in social insects
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....

. Anelosimus
Anelosimus
Anelosimus is a genus of tangle web spider described by Eugène Simon, in 1891, from Venezuela. It includes the South American social spider Anelosimus eximius and related species....

 eximius
Anelosimus eximius
Anelosimus eximius is species of social spider in the genus Anelosimus, native to the Lesser Antilles and the area from Panama to Argentina. Colonies can comprise several thousand individuals....

 (in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

) can form colonies of up to 50,000 individuals. The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

 are at least somewhat social. Members of other species in the same family but several different genera have independently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 developed social behavior. For example, although Theridion
Theridion
The spider genus Theridion, after which the family Theridiidae is named, consists of almost 600 described species that occur all around the world....

 nigroannulatum belongs to a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several Philoponella
Philoponella
Philoponella is a genus of uloborid spiders. Like all Uloboridae, these species have no venom.The species P. vicinus uses its silk to crush its victims to death.-Cooperation:...

 species (family Uloboridae), Agelena consociata
Agelena consociata
Agelena consociata is a social species of funnel web spider that occurs in tropical forests in West Africa and lives in colonies of one to several hundred individuals.-Distribution:This species is found in rainforest habitats in Gabon...

 (family Agelenidae) and Mallos
Mallos (spider)
Mallos is a spider genus belonging to the Dictynidae family.Among the genus, Mallos gregalis is known to be a social spider species, living in groups and signaling each others by vibrating their web.-External links:*...

 gregalis
Mallos gregalis
Mallos gregalis is a spider species belonging to the Dictynidae family.It is known to be a social spider species, living in groups and signaling each others by vibrating their web....

 (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 lives in small colonies which help to protect eggs and spiderlings. Even widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s (genus Latrodectus), which are notoriously aggressive and cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.

Web types


There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 in web construction, in other words use of similar techniques by remotely related species, is rampant. Non-orb web designs and the spinning behaviors that produce them have received very little attention from arachnologists, despite the fact that the majority of spiders build non-orb webs. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasp
Wasp
The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...

s, which are often the dominant predators on spiders, much prefer to attack spiders that have flat webs.

Orb webs



About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection); absorbing its momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 without breaking (stopping); and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.

The hubs of orb webs, where the spiders lurk, are usually above the center as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.

Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as: reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

s to catch insects in slow horizontal flight. However there is no single explanation for the common use of horizontal orb webs.

Spiders often attach highly visible silk bands called decorations or stabilimenta to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.

There are several unusual variants of orb web, many of them convergently evolved, including: attachment of lines to the surface of water, possibly to trap insects in or on the surface; webs with twigs through their centers, possibly to hide the spiders from predators; "ladder-like" webs that appear most effective in catching moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s. However the significance of many variations is unclear.

In 1973, Skylab 3
Skylab 3
Skylab 3 was the second manned mission to Skylab. The Skylab 3 mission started July 28, 1973, with the launch of three astronauts on the Saturn IB rocket, and lasted 59 days, 11 hours and 9 minutes...

 took two orb-web spiders into space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

 to test their web-spinning capabilities in zero gravity. At first both produced rather sloppy webs, but they adapted quickly.

Tangleweb / cobweb spiders



Members of the family Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

 weave irregular, tangled, three-dimensional webs, popularly known as cobwebs.There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.

Other types of webs


The Linyphiidae
Linyphiidae
Linyphiidae is a family of spiders, including more than 4,300 described species in 578 genera worldwide. This makes Linyphiidae the second largest family of spiders after the Salticidae. New species are still being discovered throughout the world, and the family is poorly known...

 generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall on to the sheet or are shaken on to it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.

Fossil record



Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...

. The oldest known amber that contains fossil arthropods dates from in the Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....

n, places where conditions were exceptionally suited to preserving fairly soft tissues.


The oldest known arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

 is the trigonotarbid Palaeotarbus jerami, from about in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 period, and had a triangular cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and segmented abdomen, as well as eight legs and a pair of pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. Attercopus
Attercopus
Previously interpreted as the world's oldest spider, Attercopus fimbriunguis belongs to an extinct order of arachnids named Uraraneida; thought to be close to the origins of spiders...

 fimbriunguis, from in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider. However these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica
Nephila jurassica
Nephila jurassica is an extinct species of spider in the family Nephilidae, which contains the golden silk orb-weavers. The species is known only from the Middle Jurassic Jiulongshan Formation, part of the Daohugou Beds, near the village of Daohugou in Ningcheng County, northeastern China.-History...

, from about , recorded from Daohuogo, Inner Mongolia
Inner Mongolia
Inner Mongolia is an autonomous region of the People's Republic of China, located in the northern region of the country. Inner Mongolia shares an international border with the countries of Mongolia and the Russian Federation...

 in China.

Several Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 spiders were members of the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, a primitive group now represented only by the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

.
The mesothelid Paleothele montceauensis, from the Late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 over , had five spinnerets. Although the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period saw rapid diversification
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...

 of flying insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, there are very few fossil spiders from this period.

The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 well before . Some Triassic mygalomorphs appear to be members of the family Hexathelidae
Hexathelidae
The spider family Hexathelidae, the only family in the super-family Hexatheloidea, is one of two families of spiders known as funnel-webs...

, whose modern members include the notorious Sydney funnel-web spider
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

 account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 periods provide a large number of fossil spiders, including representatives of many modern families.

Family tree



It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms which form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 on the right is based on J.W. Shultz' analysis (2007). Other views include proposals that: scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are more closely related to the extinct marine scorpion-like eurypterid
Eurypterid
Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...

s than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.

Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 feeding system. Instead they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s that are specially adapted for sperm transfer.

Taxonomy




Spiders are divided into two sub-orders, Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and Opisthothelae
Opisthothelae
Opisthothelae is a taxon within Order Araneae, consisting of the Mygalomorphae and the Araneomorphae, but excluding the Mesothelae. Opisthothelae is sometimes presented as an unranked clade and sometimes as a suborder of the Araneae...

, of which the latter contains two infra-orders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

. Over 40,000 living species of spiders (order Araneae) have been identified and are currently grouped into about 110 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 and about 3,700 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 by arachnologists
Arachnology
Arachnology is the scientific study of spiders and related animals such as scorpions, pseudoscorpions, harvestmen, collectively called arachnids. However, the study of ticks and mites is sometimes not included in arachnology, but is called Acarology...

.
  Spider diversity Features
Sub-order Species Genera Families Segmented plates on top of abdomen Ganglia in abdomen Spinnerets Striking direction of fangs
Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

87 5 1 Yes Yes Four pairs, in some species one pair fused, under middle of abdomen Downwards and forwards
Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

2,600 300 15 No, but yes in some fossils No One, two or three pairs under rear of abdomen
Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

37,000 3,400 93 From sides to center, like pincers

Mesothelae




The only living members of the primitive Mesothelae are the family Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, found only in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. Most of the Liphistiidae construct silk-lined burrows with thin trapdoor
Trapdoor
A trapdoor is a door set into a floor or ceiling .Originally, trapdoors were sack traps in mills, and allowed the sacks to pass up through the mill while naturally falling back to a closed position....

s, although some species of the genus Liphistius
Liphistius
Liphistius is a genus of basal trapdoor spiders in the family Liphistiidae. They are found in Japan, China, and Southeast Asia.-Biology:...

 build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus Liphistius run silk "tripwire
Tripwire
A tripwire is a passive triggering mechanism. Typically, a wire or cord is attached to some device for detecting or reacting to physical movement...

s" outwards from their tunnels to help them detect approaching prey, while those of genus Heptathela
Heptathela
Heptathela is a genus of spiders that includes the Kimura-gumo. They are basal trapdoor spiders of the family Liphistiidae and are found in Japan, China, and Southeast Asia.Females are up to 25 mm long, males slightly smaller...

 do not and instead rely on their built-in vibration sensors. Spiders of the genus Heptathela have no venom glands although they do have venom gland outlets on the fang tip.

The extinct families Arthrolycosidae
Arthrolycosidae
Arthrolycosidae is an extinct family of primitive spiders that bear some resemblance to the wolf spiders....

, found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 rocks, and Arthromygalidae
Arthromygalidae
The Arthromygalidae are an extinct family of primitive spiders that bear some resemblance to the tarantulas, at its peak in the Carboniferous, some 280 million years ago....

, so far found only in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks, have been classified as members of the Mesothelae.

Mygalomorphae




The Mygalomorphae, which first appeared in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 period, are generally heavily built and hairy, with large, robust chelicerae and fangs. Well-known examples include tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s, trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s and the Australasian funnel-web spider
Australasian funnel-web spider
Australian funnel-web spiders are venomous spiders of the family Hexathelidae, represented by 31 described species of Hadronyche, four Bymainiella spp., two Teranodes and monotyptic genera Plesiothera fentoni and Ilawarra whisharti...

s. Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "balloon" by using air currents for transport, their populations often form clumps. In addition to arthropods, mygalomorphs prey on frogs and lizards, and snails.

Araneomorphae




In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the "true spiders", include orb-web spiders, the cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...

 wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, and jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, as well as the only known herbivorous spider, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment.

Spider bites


Most spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting. Most of those with medically serious bites, such as recluse spider
Recluse spider
The recluse spiders or brown spiders , also known as fiddle-back, violin spiders or reapers, are a venomous genus of spiders known for their necrotic bite, which sometimes produces a characteristic set of symptoms known as Loxoscelism...

s and widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s, are shy and bite only when they feel threatened, although this can easily arise by accident. Funnel web spiders
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

' defensive tactics are aggressive and their venom, although they rarely inject much, has resulted in 13 known human deaths. On the other hand, the Brazilian wandering spider
Brazilian wandering spider
Phoneutria, commonly known as Brazilian wandering spiders, armed spiders , or banana spiders , are a genus of aggressive and highly venomous spiders found in tropical South and Central America...

 requires very little provocation.

There were about 100 reliably reported deaths from spider bites in the 20th century, but about 1,500 from jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

 stings. Many alleged cases of spider bites may represent incorrect diagnoses, which would make it more difficult to check the effectiveness of treatments for genuine bites.

Benefits to humans


Cooked tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

 spiders are considered a delicacy in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...

, and by the Piaroa
Piaroa
The Piaroa are an indigenous American ethnic group living along the banks of the Orinoco River and its tributaries in present day Venezuela, and in a few scattered locations elsewhere in Venezuela and in Colombia...

 Indians of southern Venezuela – provided the highly irritant hairs, the spiders' main defense system, are removed first.

Spider venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

s may be a less polluting alternative to conventional pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s as they are deadly to insects but the great majority are harmless to vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s. Australian funnel web spiders are a promising source as most of the world's insect pests have had no opportunity to develop any immunity
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...

 to their venom, and funnel web spiders thrive in captivity and are easy to "milk". It may be possible to target specific pests by engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

 genes for the production of spider toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s into virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es that infect species such as cotton bollworm
Cotton bollworm
Cotton bollworm may refer to:* Helicoverpa zea* Helicoverpa armigera, the American bollworm or tomato grub- See also :* Bollworm...

s.

Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

, stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

s, and erectile dysfunction
Erectile dysfunction
Erectile dysfunction is sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual performance....

.

Because spider silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 is both light and very strong, attempts
BioSteel
BioSteel is a trademark name for a high-strength based fiber material made of the recombinant spider silk-like protein extracted from the milk of transgenic goats, made by Nexia Biotechnologies....

 are being made to produce it in goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s' milk and in the leaves of plants, by means of genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

. Fine transparent spider silk fibers are used by physicists, working on optical communications, to introduce minute diffraction patterns over propagating N-slit interferometric signals
N-Slit interferometer
The N-slit interferometer is an extension of the double-slit interferometer also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton...

.

Arachnophobia


Arachnophobia
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

 is a specific phobia
Specific phobia
A specific phobia is a generic term for any kind of anxiety disorder that amounts to an unreasonable or irrational fear related to exposure to specific objects or situations...

, an abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It is one of the most common specific phobias, and some statistics show that 50% of women and 10% of men show symptoms.

It may be an exaggerated form of an instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...

ive response that helped early humans to survive, or perhaps a cultural phenomenon that is most common in predominantly European societies.

Spiders in symbolism and culture


Spiders have been the focus of fears
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

, stories and mythologies of various cultures for centuries. They have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice for the painful death their venom causes.

Web-spinning also caused the association of the spider with creation myths as they seem to have the ability to produce their own worlds. The Moche
Moche
'The Moche civilization flourished in northern Peru from about 100 AD to 800 AD, during the Regional Development Epoch. While this issue is the subject of some debate, many scholars contend that the Moche were not politically organized as a monolithic empire or state...

 people of ancient Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

 worshipped nature. They placed emphasis on animals and often depicted spiders in their art.

See also


  • Endangered spiders
    Endangered spiders
    An endangered species is “a species at risk of extinction because of human activity, changes in climate, changes in predator-prey ratios, etc., especially when officially designated as such by a governmental agency such as the U.S. Fish and Wildlife Service”...

  • Identifying spiders
    Spider taxonomy
    Spider taxonomy is the alpha taxonomy of the spiders, members of the Araneae order of the arthropod class Arachnida with about 40,000 described species. However there are likely many species that have escaped the human eye to this day, and many specimens stored in collections waiting to be...

  • Spider diversity
  • Arachnidism
    Arachnidism
    Arachnidism is a medical condition, simply defined as envenomation by a spider bite, which, depending on the species, will have various effects. Bites from the widow spiders produce a condition known as Latrodectism, while bites from the recluse spiders cause Loxoscelism...

  • Toxins

Footnotes


Spiders (order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Araneae) are air-breathing arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s that have eight legs, and chelicerae with fangs that inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 with the exception of air and sea colonization. As of 2008, approximately 40,000 spider species, and 109 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 have been recorded by taxonomists
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

; however, there has been confusion within the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

 as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.

Anatomically, spiders differ from other arthropods in that the usual body segments
Segmentation (biology)
Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 are fused into two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

, and joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

. Unlike insects, spiders do not have antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

. In all except the most primitive group, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 from up to six types of silk glands within their abdomen. Spider web
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....

s vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s with silk-producing spigots appear in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period about , but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks from , and are very similar to the most primitive surviving order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

, the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

. The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic period, before .

A herbivorous species, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

, was described in 2008, but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lasso
Lasso
A lasso , also referred to as a lariat, riata, or reata , is a loop of rope that is designed to be thrown around a target and tighten when pulled. It is a well-known tool of the American cowboy. The word is also a verb; to lasso is to successfully throw the loop of rope around something...

ing it with sticky bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, and they liquidize their food by flooding it with digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s and grinding it with the bases of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, as they do not have true jaws.

Male spiders identify themselves by a variety of complex courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to avoid being eaten by the females. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the aggressive widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and other mygalomorph
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 spiders can live up to 25 years in captivity.

While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s. Spider silk provides a combination of lightness, strength and elasticity
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....

 that is superior to that of synthetic materials, and spider silk genes have been inserted into mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology
Mythology
The term mythology can refer either to the study of myths, or to a body or collection of myths. As examples, comparative mythology is the study of connections between myths from different cultures, whereas Greek mythology is the body of myths from ancient Greece...

 symbolizing various combinations of patience, cruelty and creative powers.

Body plan




Spiders are chelicerates and therefore arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s. As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 made of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

 and proteins; heads that are composed of several segments that fuse during the development of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. Being chelicerates, their bodies consist of two tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...

, sets of segments that serve similar functions: the foremost one, called the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 or prosoma, is a complete fusion of the segments that in an insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 would form two separate tagmata, the head and thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

; the rear tagma is called the abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 or opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...

. In spiders the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

 typical of most arthropods. In fact chelicerates' only appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, and serve different functions within different groups of chelicerates.


Spiders and scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are members of one chelicerate group, the arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fang
Fang
Fang is a mammal's canine tooth.Fang may also refer to:* A snake's poison-injecting tooth: see snake venom* Fang people, in Central Africa* Fang language, spoken by Fang people...

s that are generally venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

ous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition those of male spiders have enlarged last sections used for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 transfer.

In spiders the cephalothorax and abdomen are joined by a small, cylindrical pedicel
Pedicel (spider)
The pedicel of a spider is a small, flexible cylinder that joins the cephalothorax and abdomen. This helps the spider to spin silk without moving the cephalothorax....

, which enables the abdomen to move independently when producing silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

. The upper surface of the cephalothorax is covered by a single, convex carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, whose living members are the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, have segmented plates on the upper surface.

Circulation and respiration



Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

s. The blood of many spiders that have book lung
Book lung
A book lung is a type of respiration organ used for atmospheric gas exchange and is found in arachnids, such as scorpions and spiders. Each of these organs is found inside a ventral abdominal cavity and connects with the surroundings through a small opening. Book lungs are not related to the lungs...

s contains the respiratory pigment
Respiratory pigment
A respiratory pigment is a molecule, such as hemoglobin in humans, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, haemocyanin, haemerythrin and chlorocruorin...

 hemocyanin
Hemocyanin
Hemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...

 to make oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 transport more efficient.

Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....

 system, or both. Mygalomorph and Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. This is also the case for some basal araneomorph spiders like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The trachea system has most likely evolved in small ancestors to help resist desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

. The trachea were originally connected to the surroundings through a pair of openings called spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

s, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets. Spiders that have tracheae generally have higher metabolic rates and better water conservation.

Feeding, digestion and excretion



Uniquely among chelicerates, the final sections of spiders' chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 are fangs, and the great majority of spiders can use them to inject venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

 into prey from venom gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s in the roots of the chelicerae. Like most arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s including scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s, while flooding it with enzymes; in these species the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.

The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.

Most spiders convert nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

ous waste products into uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...

, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

l chamber, from which they are expelled through the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 lineages that can live far away from water, for example the tubules of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s and arachnids develop from completely different parts of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

. However a few primitive spiders, the sub-order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and infra-order Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

, retain the ancestral arthropod nephridia ("little kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s"), which use large amounts of water to excrete nitrogenous waste products as ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

.

Central nervous system


The basic arthropod central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 consists of a pair of nerve cord
Ventral nerve cord
The ventral nerve cord makes up the nervous system of some phyla of the invertebrates, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral plane of the organism...

s running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

 is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, of which the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

 are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.

Eyes



Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum
Tapetum lucidum
The tapetum lucidum is a layer of tissue in the eye of many vertebrate animals....

, and wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s can be spotted by torch light reflected from the tapeta. On the other hand jumping spiders' secondary eyes have no tapeta. Jumping spiders' visual acuity
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....

 exceeds by a factor of ten that of dragonflies
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

, which have by far the best vision among insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.

Other senses


As with other arthropods, spiders' cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

s would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

 and smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

, often by means of setae. Spiders also have in the joints of their limbs slit sensilla
Slit sensilla
The slit sensilla is a small mechanoreceptory organ in the exoskeleton of spiders which detects strain due to forces experienced by the animal. As the name indicates, a slit sensilla is a small groove in the exoskeleton which deforms under stress, and these deformations are detected by neurons...

e that detect forces and vibrations. In web-building spiders all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.

Like most arthropods, spiders lack balance and acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand little is known about what other internal sensors spiders or other arthropods may have.

Locomotion


Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. As a result a spider with a punctured cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs.

Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

s, keep at least four legs on the surface while walking or running.

Silk production



The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

. Each spinneret has many spigots, each of which is connected to one silk gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

. There are at least six types of silk gland, each producing a different type of silk.

Silk is mainly composed of a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 to nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 and biological materials such as chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

, collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 and cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

, but is much more elastic, in other words it can stretch much further before breaking or losing shape.

Some spiders have a cribellum
Cribellum
The cribellum is a silk spinning organ found in certain spiders. Unlike normal spinnerets, the cribellum consists of one or more plates covered in thousands of tiny spigots. These spigots produce extremely fine fibers which are combed out by the spider's calamistrum, producing silk with a wooly...

, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum
Calamistrum
In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are...

, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However most modern groups of spiders have lost the cribellum.

Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 and for fertilized eggs; as a "safety rope
Safety harness
A safety harness is a form of protective equipment designed to protect a person, animal, or object from injury or damage. The harness is an attachment between a stationary and non-stationary object and is usually fabricated from rope, cable or webbing and locking hardware...

"; for nest-building; and as "parachute
Parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

s" by the young of some species.

Reproduction and life cycle


Spiders reproduce sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...

ually and fertilization is internal
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

 but indirect, in other words the sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, male spiders do not produce ready-made spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

s (packages of sperm) but spin small sperm webs on to which they ejaculate and then transfer the sperm to syringe
Syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...

-like structures on the tips of their pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell".


Spiders generally use elaborate courtship
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...

 rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, which have excellent eyesight. If courtship is successful, the male injects his sperm from the pedipalps into the female's genital opening, known as the epigyne
Epigyne
The epigyne or epigynum is the external genital structure of female spiders. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species...

, on the underside of her abdomen. Female's reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.

Males of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Tidarren
Tidarren
Tidarren is a genus of spiders. The males are much smaller than females.The males of this genus amputate one of their palps before maturation and enter their adult life with one palp only...

 amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....

i species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male. In over 60% of cases the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.

Females lay up to 3,000 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 in one or more silk egg sacs, which maintain a fairly constant humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

 level. In some species the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...

 or attaching them to the spinnerets and dragging them along.

Baby spiders pass all their larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

l stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...

 food.

Like other arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, spiders have to molt to grow as their cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...

 ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s can live in captivity for over 20 years.


Size


Spiders occur in a large range of sizes. The smallest, Patu digua
Patu digua
Patu digua is by some accounts considered to be the smallest spider in the world, with males reaching a body size of about 0.37 mm. Small as the head of a pin. However, there are other spider species of similar size where only the female is known. Because male spiders are usually smaller than...

 from Colombia, are less than 0.37 mm (0.0145669291338583 in) in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm (3.5 in) and leg spans up to 250 mm (10 in).

Coloration


Only three classes of pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 (ommochrome
Ommochrome
Ommochrome refers to several biological pigments that occur in the eyes of crustaceans and insects. The eye color is determined by the ommochromes. Ommochromes are also found in the chromatophores of cephalopods, and in spiders....

s, bilins
Bilin (biochemistry)
Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrins. Bilin was named as a bile pigment of mammals, but can also be found in lower vertebrates, invertebrates, as well as red algae, green plants and cyanobacteria...

 and guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

) have been identified in spiders, although other pigments have been detected but not yet characterized. Melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

s, carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...

s and pterin
Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a keto group and an amino group on positions 4 and 2 respectively...

s, very common in other animals, are apparently absent. In some species the exocuticle of the legs and prosoma is modified by a tanning
Tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

 process, resulting in brown coloration.
Bilins are found, for example, in Micrommata virescens
Micrommata virescens
The green huntsman spider is a spider of the family Sparassidae. It does not build a web, and hunts insects in green vegetation, where it is well camouflaged....

, resulting in its green color. Guanine is responsible for the white markings of the European garden spider
European garden spider
The European garden spider, diadem spider, cross spider, or cross orbweaver is a very common and well-known orb-weaver spider in Europe and parts of North America, in a range extending from New England and the Southeast to California and the northwestern United States and adjacent parts of...

 Araneus diadematus. It is in many species accumulated in specialized cells called guanocytes. In genera such as Tetragnatha
Tetragnatha
Tetragnatha is a genus of spiders containing hundreds of species. They are found all over the world, although most occur in the tropics and subtropics. They are commonly called stretch spiders, referring to their elongated body form...

, Leucauge
Leucauge
Leucauge is a spider genus with pantropical distribution.The body and leg shapes and the silver, black and yellow markings of Leucauge females make identification of the genus relatively easy. They have two rows of long, slender curved hairs on the femurs of the fourth leg...

, Argyrodes
Argyrodes
Spiders of the genus Argyrodes , also called dewdrop spiders, occur worldwide. They are best known as kleptoparasites: they steal other spiders' prey. They invade and reside in their host's web even though they can spin their own webs...

 or Theridiosoma, guanine creates their silvery appearance. While guanine is originally an end-product of protein metabolism, its excretion can be blocked in spiders, leading to an increase in its storage. Structural colors occur in some species, which are the result of the diffraction, scattering or interference of light, for example by modified setae or scales. The white prosoma of Argiope
Argiope (spider)
The genus Argiope includes rather large and spectacular spiders that have often a strikingly coloured abdomen. These are well distributed throughout the world, and most countries in temperate or warmer climates have one or more species, which look similar....

 results from hairs reflecting the light, Lycosa
Lycosa
Lycosa is a genus of wolf spiders. More than 200 species are found, represented throughout most of the world. Often called the "true tarantula", Lycosa can be distinguished from common wolf spiders by their relatively large size...

 and Josa
Josa
Josa is a municipality located in the province of Teruel, Aragon, Spain. According to the 2004 census , the municipality has a population of 30 inhabitants....

 both have areas of modified cuticle that act as light reflectors.

Non-predatory feeding


Although spiders are generally regarded as predatory, the jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

 Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 gets over 90% of its food from fairly solid plant material produced by acacia
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...

s as part of a mutually beneficial relationship with a species of ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...

.

Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been under-estimated. Nectar contains amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s, vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...

s and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.

Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....

s, marmalade
Marmalade
Marmalade is a fruit preserve made from the juice and peel of citrus fruits, boiled with sugar and water. The benchmark citrus fruit for marmalade production in Britain is the "Seville orange" from Spain, Citrus aurantium var...

, milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 and sausages.

Methods of capturing prey




The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.

Females of the water spider Argyroneta aquatica build underwater "diving bell" webs which they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.

Net-casting spiders weave only small webs but then manipulate them to trap prey. Those of the genus Hyptiotes
Hyptiotes
-Feeding:Hyptiotes creates a triangular web and sits at a vertex until it detects vibrations that signify the collision of its prey. At this moment hyptiotes releases a coil of silk which it has held taught in such a manner that the tension of the web causes it to entangle the spider's prey. The...

 and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae
Deinopidae
The spider family Deinopidae consists of stick-like elongate spiders that build unusual webs that they suspend between the front legs. When prey approaches, the spider will stretch the net to two or three times its relaxed size and propel itself onto the prey, entangling it in the web...

 weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis
Deinopis
Deinopis is a genus of net-casting spiders.-Name:The genus name is derived from the Greek deinos "fearful" and opis "appearance"; see also the family name "ogre-faced" spiders.-Species:...

 spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa
Deinopis subrufa
Deinopis subrufa is a species of net-casting spiders. It occurs in eastern Australia and Tasmania. It is a nocturnal hunter, having excellent eyesight, and hunts using a silken net to capture its prey. They feed on a variety of insects - ants, beetles, crickets and other spiders...

 appears to live mainly on tipulid flies that they catch with the backwards strike.

Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas
Bolas
Bolas are a throwing weapon superficially similar to the surujin, made of weights on the ends of interconnected cords, designed to capture animals by entangling their legs...

 made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...

s of moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.


The primitive Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, the "trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s" (family Ctenizidae) and many tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s are ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...

s that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...

s, which see ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, fishing spiders and some crab spider
Crab spider
Crab spider is a common name applied loosely to many species of spiders, but most nearly consistently to members of the family Thomisidae...

s capture prey by chasing it, and rely mainly on vision to locate prey.


Some jumping spiders of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Portia hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that Portias instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators.


Ant-mimicking
Ant mimicry
Ant mimicry is mimicry of ants by other organisms. Ants are abundant all over the world, and insect predators that rely on vision to identify their prey such as birds and wasps normally avoid them, either because they are unpalatable, or aggressive. Thus some other arthropods mimic ants to escape...

 spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in form to their heads to mimic antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna
Synemosyna
Synemosyna is a genus of ant-like jumping spiders that occurs from Argentina to the northern United States.-Species:* Synemosyna americana — Mexico to Venezuela* Synemosyna ankeli Cutler & Müller, 1991 — Colombia...

 walk on the outer edges of leaves in the same way as Pseudomyrmex
Pseudomyrmex
Pseudomyrmex is a genus of stinging, wasp-like ants in the family Formicidae . They are large eyed, slender ants with an arboreal habitat. They are found exclusively in the New World in tropical and subtropical regions...

. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

", such as aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...

s. When at rest, the ant-mimicking crab spider Amyciaea
Amyciaea
Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey .-Species:* Amyciaea albomaculata * Amyciaea forticeps Amyciaea is a genus of crab spiders that mimics ants, their preferred prey.A. albomaculata mimics its weaver ant prey...

 does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.

Defense


There is strong evidence that spiders' coloration is camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...

 that helps them to evade their major predators, birds and parasitic wasp
Parasitic wasp
The term parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. They are primarily parasitoids of other animals, mostly other arthropods...

s, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator
Theridion grallator
Theridion grallator, also known as the "happy face spider," is a member of the Theridiidae family.The Hawaiian name is nananana makakii...

, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...

 to offer much benefit. However a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.

Many of the family Theraphosidae, which includes tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s and baboon spiders, have urticating hair
Urticating hair
Urticating hairs, i.e. stinging hairs, are one of the primary defense mechanisms used by numerous plants, some New World tarantulas, and various lepidopteran caterpillars. Urtica is Latin for "nettle", and hairs that urticate are characteristic of this type of plant, and many other plants in...

s on their abdomens and use their legs to flick them at attackers. These hairs are fine seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, Carparachne aureoflava
Wheel spider
The Wheel spider, Golden Wheel spider, or Dancing White lady spider , is a huntsman spider native to the Namib Desert of Southern Africa...

, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling
Cartwheel (gymnastics)
In gymnastics, a cartwheel is a sideways rotary movement performed by bringing the hands to the ground while the body inverts and the legs travel over the body, coming down to a standing position.-Terminology:...

 down sand dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...

s.

Social spiders



A few species of spiders that build webs live together in large colonies and show social behavior, although not as complex as in social insects
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....

. Anelosimus
Anelosimus
Anelosimus is a genus of tangle web spider described by Eugène Simon, in 1891, from Venezuela. It includes the South American social spider Anelosimus eximius and related species....

 eximius
Anelosimus eximius
Anelosimus eximius is species of social spider in the genus Anelosimus, native to the Lesser Antilles and the area from Panama to Argentina. Colonies can comprise several thousand individuals....

 (in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

) can form colonies of up to 50,000 individuals. The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

 are at least somewhat social. Members of other species in the same family but several different genera have independently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 developed social behavior. For example, although Theridion
Theridion
The spider genus Theridion, after which the family Theridiidae is named, consists of almost 600 described species that occur all around the world....

 nigroannulatum belongs to a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several Philoponella
Philoponella
Philoponella is a genus of uloborid spiders. Like all Uloboridae, these species have no venom.The species P. vicinus uses its silk to crush its victims to death.-Cooperation:...

 species (family Uloboridae), Agelena consociata
Agelena consociata
Agelena consociata is a social species of funnel web spider that occurs in tropical forests in West Africa and lives in colonies of one to several hundred individuals.-Distribution:This species is found in rainforest habitats in Gabon...

 (family Agelenidae) and Mallos
Mallos (spider)
Mallos is a spider genus belonging to the Dictynidae family.Among the genus, Mallos gregalis is known to be a social spider species, living in groups and signaling each others by vibrating their web.-External links:*...

 gregalis
Mallos gregalis
Mallos gregalis is a spider species belonging to the Dictynidae family.It is known to be a social spider species, living in groups and signaling each others by vibrating their web....

 (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

 lives in small colonies which help to protect eggs and spiderlings. Even widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s (genus Latrodectus), which are notoriously aggressive and cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.

Web types


There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 in web construction, in other words use of similar techniques by remotely related species, is rampant. Non-orb web designs and the spinning behaviors that produce them have received very little attention from arachnologists, despite the fact that the majority of spiders build non-orb webs. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasp
Wasp
The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...

s, which are often the dominant predators on spiders, much prefer to attack spiders that have flat webs.

Orb webs



About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection); absorbing its momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 without breaking (stopping); and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.

The hubs of orb webs, where the spiders lurk, are usually above the center as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.

Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as: reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

s to catch insects in slow horizontal flight. However there is no single explanation for the common use of horizontal orb webs.

Spiders often attach highly visible silk bands called decorations or stabilimenta to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.

There are several unusual variants of orb web, many of them convergently evolved, including: attachment of lines to the surface of water, possibly to trap insects in or on the surface; webs with twigs through their centers, possibly to hide the spiders from predators; "ladder-like" webs that appear most effective in catching moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

s. However the significance of many variations is unclear.

In 1973, Skylab 3
Skylab 3
Skylab 3 was the second manned mission to Skylab. The Skylab 3 mission started July 28, 1973, with the launch of three astronauts on the Saturn IB rocket, and lasted 59 days, 11 hours and 9 minutes...

 took two orb-web spiders into space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

 to test their web-spinning capabilities in zero gravity. At first both produced rather sloppy webs, but they adapted quickly.

Tangleweb / cobweb spiders



Members of the family Theridiidae
Theridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...

 weave irregular, tangled, three-dimensional webs, popularly known as cobwebs.There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.

Other types of webs


The Linyphiidae
Linyphiidae
Linyphiidae is a family of spiders, including more than 4,300 described species in 578 genera worldwide. This makes Linyphiidae the second largest family of spiders after the Salticidae. New species are still being discovered throughout the world, and the family is poorly known...

 generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall on to the sheet or are shaken on to it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.

Fossil record



Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...

. The oldest known amber that contains fossil arthropods dates from in the Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....

n, places where conditions were exceptionally suited to preserving fairly soft tissues.


The oldest known arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

 is the trigonotarbid Palaeotarbus jerami, from about in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 period, and had a triangular cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

 and segmented abdomen, as well as eight legs and a pair of pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s. Attercopus
Attercopus
Previously interpreted as the world's oldest spider, Attercopus fimbriunguis belongs to an extinct order of arachnids named Uraraneida; thought to be close to the origins of spiders...

 fimbriunguis, from in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider. However these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica
Nephila jurassica
Nephila jurassica is an extinct species of spider in the family Nephilidae, which contains the golden silk orb-weavers. The species is known only from the Middle Jurassic Jiulongshan Formation, part of the Daohugou Beds, near the village of Daohugou in Ningcheng County, northeastern China.-History...

, from about , recorded from Daohuogo, Inner Mongolia
Inner Mongolia
Inner Mongolia is an autonomous region of the People's Republic of China, located in the northern region of the country. Inner Mongolia shares an international border with the countries of Mongolia and the Russian Federation...

 in China.

Several Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 spiders were members of the Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

, a primitive group now represented only by the Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

.
The mesothelid Paleothele montceauensis, from the Late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 over , had five spinnerets. Although the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period saw rapid diversification
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...

 of flying insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, there are very few fossil spiders from this period.

The main groups of modern spiders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

, first appear in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 well before . Some Triassic mygalomorphs appear to be members of the family Hexathelidae
Hexathelidae
The spider family Hexathelidae, the only family in the super-family Hexatheloidea, is one of two families of spiders known as funnel-webs...

, whose modern members include the notorious Sydney funnel-web spider
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

 account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 periods provide a large number of fossil spiders, including representatives of many modern families.

Family tree



It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms which form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 on the right is based on J.W. Shultz' analysis (2007). Other views include proposals that: scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s are more closely related to the extinct marine scorpion-like eurypterid
Eurypterid
Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...

s than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.

Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

 feeding system. Instead they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

s that are specially adapted for sperm transfer.

Taxonomy




Spiders are divided into two sub-orders, Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

 and Opisthothelae
Opisthothelae
Opisthothelae is a taxon within Order Araneae, consisting of the Mygalomorphae and the Araneomorphae, but excluding the Mesothelae. Opisthothelae is sometimes presented as an unranked clade and sometimes as a suborder of the Araneae...

, of which the latter contains two infra-orders, Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

 and Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

. Over 40,000 living species of spiders (order Araneae) have been identified and are currently grouped into about 110 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 and about 3,700 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 by arachnologists
Arachnology
Arachnology is the scientific study of spiders and related animals such as scorpions, pseudoscorpions, harvestmen, collectively called arachnids. However, the study of ticks and mites is sometimes not included in arachnology, but is called Acarology...

.
  Spider diversity Features
Sub-order Species Genera Families Segmented plates on top of abdomen Ganglia in abdomen Spinnerets Striking direction of fangs
Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....

87 5 1 Yes Yes Four pairs, in some species one pair fused, under middle of abdomen Downwards and forwards
Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...

2,600 300 15 No, but yes in some fossils No One, two or three pairs under rear of abdomen
Araneomorphae
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...

37,000 3,400 93 From sides to center, like pincers

Mesothelae




The only living members of the primitive Mesothelae are the family Liphistiidae
Liphistiidae
The spider family Liphistiidae comprises 5 genera and 85 species from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae...

, found only in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. Most of the Liphistiidae construct silk-lined burrows with thin trapdoor
Trapdoor
A trapdoor is a door set into a floor or ceiling .Originally, trapdoors were sack traps in mills, and allowed the sacks to pass up through the mill while naturally falling back to a closed position....

s, although some species of the genus Liphistius
Liphistius
Liphistius is a genus of basal trapdoor spiders in the family Liphistiidae. They are found in Japan, China, and Southeast Asia.-Biology:...

 build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus Liphistius run silk "tripwire
Tripwire
A tripwire is a passive triggering mechanism. Typically, a wire or cord is attached to some device for detecting or reacting to physical movement...

s" outwards from their tunnels to help them detect approaching prey, while those of genus Heptathela
Heptathela
Heptathela is a genus of spiders that includes the Kimura-gumo. They are basal trapdoor spiders of the family Liphistiidae and are found in Japan, China, and Southeast Asia.Females are up to 25 mm long, males slightly smaller...

 do not and instead rely on their built-in vibration sensors. Spiders of the genus Heptathela have no venom glands although they do have venom gland outlets on the fang tip.

The extinct families Arthrolycosidae
Arthrolycosidae
Arthrolycosidae is an extinct family of primitive spiders that bear some resemblance to the wolf spiders....

, found in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 rocks, and Arthromygalidae
Arthromygalidae
The Arthromygalidae are an extinct family of primitive spiders that bear some resemblance to the tarantulas, at its peak in the Carboniferous, some 280 million years ago....

, so far found only in Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 rocks, have been classified as members of the Mesothelae.

Mygalomorphae




The Mygalomorphae, which first appeared in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 period, are generally heavily built and hairy, with large, robust chelicerae and fangs. Well-known examples include tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

s, trapdoor spider
Trapdoor spider
Trapdoor spiders are medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. Some similar species are also called trapdoor spiders, such as the Liphistiidae, Barychelidae, Cyrtaucheniidae and some Idiopidae and Nemesiidae...

s and the Australasian funnel-web spider
Australasian funnel-web spider
Australian funnel-web spiders are venomous spiders of the family Hexathelidae, represented by 31 described species of Hadronyche, four Bymainiella spp., two Teranodes and monotyptic genera Plesiothera fentoni and Ilawarra whisharti...

s. Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "balloon" by using air currents for transport, their populations often form clumps. In addition to arthropods, mygalomorphs prey on frogs and lizards, and snails.

Araneomorphae




In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the "true spiders", include orb-web spiders, the cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...

 wolf spider
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...

s, and jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...

s, as well as the only known herbivorous spider, Bagheera kiplingi
Bagheera kiplingi
Bagheera kiplingi is a species of jumping spider found in Central America including Mexico, Costa Rica and Guatemala. It is the type species of the genus Bagheera, which includes one other species, B. prosper. B. kiplingi is notable for its peculiar diet, which, uniquely for a spider, is mostly...

. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment.

Spider bites


Most spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting. Most of those with medically serious bites, such as recluse spider
Recluse spider
The recluse spiders or brown spiders , also known as fiddle-back, violin spiders or reapers, are a venomous genus of spiders known for their necrotic bite, which sometimes produces a characteristic set of symptoms known as Loxoscelism...

s and widow spider
Widow spider
Latrodectus is a genus of spider, in the family Theridiidae, which contains 31 recognized species. The common name widow spiders is sometimes applied to members of the genus due to the behavior of the female of eating the male after mating, although sometimes the males of some species are not eaten...

s, are shy and bite only when they feel threatened, although this can easily arise by accident. Funnel web spiders
Sydney funnel-web spider
The Sydney funnel-web spider, Atrax robustus, is an Australian funnel-web spider usually found within a radius of Sydney, New South Wales, Australia.-Description:...

' defensive tactics are aggressive and their venom, although they rarely inject much, has resulted in 13 known human deaths. On the other hand, the Brazilian wandering spider
Brazilian wandering spider
Phoneutria, commonly known as Brazilian wandering spiders, armed spiders , or banana spiders , are a genus of aggressive and highly venomous spiders found in tropical South and Central America...

 requires very little provocation.

There were about 100 reliably reported deaths from spider bites in the 20th century, but about 1,500 from jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

 stings. Many alleged cases of spider bites may represent incorrect diagnoses, which would make it more difficult to check the effectiveness of treatments for genuine bites.

Benefits to humans


Cooked tarantula
Tarantula
Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

 spiders are considered a delicacy in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...

, and by the Piaroa
Piaroa
The Piaroa are an indigenous American ethnic group living along the banks of the Orinoco River and its tributaries in present day Venezuela, and in a few scattered locations elsewhere in Venezuela and in Colombia...

 Indians of southern Venezuela – provided the highly irritant hairs, the spiders' main defense system, are removed first.

Spider venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

s may be a less polluting alternative to conventional pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s as they are deadly to insects but the great majority are harmless to vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s. Australian funnel web spiders are a promising source as most of the world's insect pests have had no opportunity to develop any immunity
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...

 to their venom, and funnel web spiders thrive in captivity and are easy to "milk". It may be possible to target specific pests by engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

 genes for the production of spider toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

s into virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es that infect species such as cotton bollworm
Cotton bollworm
Cotton bollworm may refer to:* Helicoverpa zea* Helicoverpa armigera, the American bollworm or tomato grub- See also :* Bollworm...

s.

Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

, stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

s, and erectile dysfunction
Erectile dysfunction
Erectile dysfunction is sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual performance....

.

Because spider silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...

 is both light and very strong, attempts
BioSteel
BioSteel is a trademark name for a high-strength based fiber material made of the recombinant spider silk-like protein extracted from the milk of transgenic goats, made by Nexia Biotechnologies....

 are being made to produce it in goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s' milk and in the leaves of plants, by means of genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...

. Fine transparent spider silk fibers are used by physicists, working on optical communications, to introduce minute diffraction patterns over propagating N-slit interferometric signals
N-Slit interferometer
The N-slit interferometer is an extension of the double-slit interferometer also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton...

.

Arachnophobia


Arachnophobia
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

 is a specific phobia
Specific phobia
A specific phobia is a generic term for any kind of anxiety disorder that amounts to an unreasonable or irrational fear related to exposure to specific objects or situations...

, an abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It is one of the most common specific phobias, and some statistics show that 50% of women and 10% of men show symptoms.

It may be an exaggerated form of an instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...

ive response that helped early humans to survive, or perhaps a cultural phenomenon that is most common in predominantly European societies.

Spiders in symbolism and culture


Spiders have been the focus of fears
Arachnophobia
Arachnophobia or arachnephobia is a specific phobia, the fear of spiders and other arachnids such as scorpions. It is a manifestation of zoophobia, among the most common of all phobias. The reactions of arachnophobics often seem irrational to others...

, stories and mythologies of various cultures for centuries. They have symbolized patience due to their hunting technique of setting webs and waiting for prey, as well as mischief and malice for the painful death their venom causes.

Web-spinning also caused the association of the spider with creation myths as they seem to have the ability to produce their own worlds. The Moche
Moche
'The Moche civilization flourished in northern Peru from about 100 AD to 800 AD, during the Regional Development Epoch. While this issue is the subject of some debate, many scholars contend that the Moche were not politically organized as a monolithic empire or state...

 people of ancient Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

 worshipped nature. They placed emphasis on animals and often depicted spiders in their art.

See also


  • Endangered spiders
    Endangered spiders
    An endangered species is “a species at risk of extinction because of human activity, changes in climate, changes in predator-prey ratios, etc., especially when officially designated as such by a governmental agency such as the U.S. Fish and Wildlife Service”...

  • Identifying spiders
    Spider taxonomy
    Spider taxonomy is the alpha taxonomy of the spiders, members of the Araneae order of the arthropod class Arachnida with about 40,000 described species. However there are likely many species that have escaped the human eye to this day, and many specimens stored in collections waiting to be...

  • Spider diversity
  • Arachnidism
    Arachnidism
    Arachnidism is a medical condition, simply defined as envenomation by a spider bite, which, depending on the species, will have various effects. Bites from the widow spiders produce a condition known as Latrodectism, while bites from the recluse spiders cause Loxoscelism...

  • Toxins

External links