Phasmatodea
Encyclopedia
The Phasmatodea are an order of insect
s, whose members are variously known as stick insects (in Europe
and Australasia
), walking sticks or stick-bugs (in the United States and Canada
), phasmids, ghost insects and leaf insects (generally the family Phylliidae
). The ordinal name is derived from the Ancient Greek
φάσμα phasma, meaning an apparition or phantom, and refers to the resemblance of many species to sticks or leaves. Their natural camouflage can make them extremely difficult to spot. Phasmatodea can be found all over the world in warmer zones, especially the tropics
and subtropics
. The greatest diversity is found in Southeast Asia
and South America
, followed by Australia
. Phasmids also have a considerable presence in the continental United States, mainly in the Southeast
.
are the world's longest insects, measuring up to 56.7 centimetres (22.3 in) in total length in the case of Phobaeticus chani
, including the outstretched legs. Females of the species Heteropteryx dilatata
are the heaviest known phasmids, possibly weighing in excess of 65 grams.
Some have cylindrical stick-like bodies, while others have a flattened, leaflike shape. The thorax
is long in the winged species, since it houses the flight muscles, but is typically much shorter in the wingless forms. Where present, the first pair of wings are narrow and cornified, while the hind wings are broad, with straight longitudinal veins and multiple cross-veins. The body is often further modified to resemble vegetation, with ridges resembling leaf veins, bark-like tubercles, and other forms of camouflage. A few species, such as Carausius morosus
, are even able to change their pigmentation to match their surroundings. Many species are wingless, or have reduced wings. The mouthparts
project out from the head. Chewing mandibles are uniform across species. The legs are typically long and slender, and some species are capable of limb autotomy
. They have long, slender antennae
that are as long or longer than the length of the body in some species.
All phasmids possess compound eyes, but ocelli are only found in some winged males. Phasmids have an impressive visual system that allow them to perceive significant detail even in dim conditions, which suits their typically nocturnal lifestyle. They are born equipped with tiny compound eyes with a limited number of facets. As the insect grows through successive molts, the number of facets is increased along with the number of photoreceptor cells in the eye. The sensitivity of the adult eye is at least tenfold that of the first instar
nymphs. As the eye grows more complex, the mechanisms to adapt to dark/light changes are also enhanced: eyes in dark conditions evidence less screening pigments, which would block light, than during the daytime, and changes in the width of the retinal layer to adapt to changes in available light are significantly more pronounced in adults. However, the larger size of the adult insect’s eyes makes them more prone to radiation damage. This explains why fully grown individuals are mostly nocturnal. Lessened sensitivity to light in the newly emerged insects helps them to escape from the leaf litter wherein they are hatched and move upward into the illuminated foliage. Young stick insects are diurnal feeders and will move around freely, expanding their foraging
range.
that both prevent an attack from happening in the first place (primary defense) and are deployed after an attack has been initiated (secondary defense).
The defense mechanism most readily identifiable with Phasmatodea is camouflage. Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as O. macklotti and Palophus centaurus) are covered in mossy or lichenous
outgrowths that supplement their disguise. Some species have the ability to change color as their surroundings shift (B. scabrinota, T. californica). In a further behavioral adaptation to supplement crypsis
, a number of species have been noted to perform a rocking motion where the body is swayed from side to side that is thought to reflect the movement of leaves or twigs swaying in the breeze. Another method by which stick insects avoid predation and resemble twigs is by feigning death (catalepsy
), where the insect enters a motionless state that can be maintained for a long period. The nocturnal feeding habits of adults also aids Phasmatodea in remaining concealed from predators.
In a seemingly opposite method of defense, many species of Phasmatodea will seek to startle the encroaching predator by flashing bright colors that are normally hidden and making a loud noise. When disturbed on a branch or foliage, some species, while dropping to the undergrowth to escape, will open their wings momentarily during free fall to display bright colors that disappear when the insect lands. Others will maintain their display for up to 20 minutes, hoping to frighten the predator and convey the appearance of a larger size. Some accompany the visual display with noise made by rubbing together parts of the wings or antennae.
Some species, such as the young nymphs of E. tiaratum, have been observed to curl the abdomen upwards over the body and head to resemble ants or scorpions in an act of mimicry, another defense mechanism by which the insects avoid becoming prey.
When threatened, some phasmids that are equipped with femoral spines on the metathoracic
legs (O. martini, Eurycantha calcarata, Eurycantha horrida, D. veiliei, D. covilleae) respond by curling the abdomen upward and repeatedly swinging the legs together, grasping at the threat. If the menace is caught, the spines can draw blood and inflict considerable pain.
A number of species are equipped with a pair of glands at the anterior edge of the prothorax
that enable the insect to release defensive secretions, including chemical compounds of varying effect: from the production of distinct odors to the causing of a stinging, burning sensation in the eyes and mouth of a predator. The spray often contains pungent-smelling volatile
metabolites, previously thought to be concentrated in the insect from its plant food sources. However, based on recent research it seems more likely that they manufacture their own chemical defense substances. Additionally, the chemistry of the defense spray from at least one species, Anisomorpha buprestoides
, has been shown to vary based on their life stage and/or population. This chemical spray variation also corresponds with regionally specific color form populations in Florida who also have distinct behaviors. The spray from one species, Megacrania nigrosulfurea, is even used as a treatment for skin infections by a tribe in Papua New Guinea
because of its antibacterial constituents. Some species employ a shorter-range defensive secretion, where individuals bleed reflexively through the joints of their legs and the seams of the exoskeleton
when bothered, allowing the blood (hemolymph
), which contains distasteful additives, to discourage predators. Stick insects, like their distant relation the grasshopper, can also discharge the contents of their stomach through vomiting when harassed, a fluid that is considered inedible by some predators.
The life cycle of the stick insect begins when the female deposits her eggs through one of three methods of oviposition
: she will either flick her egg to the ground by a movement of the ovipositor or her entire abdomen, carefully place the eggs in the axils of the host plant or bury them in small pits in the soil, or stick the eggs to a substrate
, usually a stem or leaf of the food plant. A single female lay from 100 to 1,200 eggs after mating, depending on the species. Most species of phasmid are parthenogenic, meaning that females lay eggs without needing to mate with males to produce offspring. However, some parthenogenic species retain the ability to mate and are bisexual depending on the presence and abundance of males. Eggs from virgin mothers are entirely female and exact copies of their mothers.
Phasmatodea eggs resemble seeds in shape and size, and have hard shells. They have a lid-like structure called an operculum
at the anterior pole, from which the nymph emerges during hatching. The eggs vary in the hatching period, from 13 to more than 70 days, with the average around 20-30 days. Some species, particularly those from temperate
regions, undergo diapause
, where development is delayed during the winter months. Diapause is affected by photoperiod on the egg-laying adults or can be genetically determined. Diapause is broken by exposure to the cold of winter, causing the eggs to hatch during the following spring. Among species of economic importance, diapause affects the development of 2-year cycles of outbreaks.
Many species' eggs bear a fatty knoblike capitulum that caps the operculum. This structure attracts ants because of its resemblance to the elaiosome
of some plant seeds that is a sought after food source for ant larvae, and usually contributes to ensuring seed dispersal by ants, a form of ant-plant mutualism called myrmecochory
. The ants take the egg into their nest underground and can remove the capitulum to feed to their larvae without harming the phasmid embryo. There, the egg hatches and the young nymph, which initially resembles an ant (another instance of mimicry among phasmatodea), eventually emerges from the nest and climbs the nearest tree to safety in the foliage.
The Phasmatodea life cycle is hemimetabolous, proceeding through a series of several nymphal instars. The stick insect’s wings develop externally. As is the case with hatching, if the nymph is caught in the encasing of a rejected cast skin (or shell), it will likely die because it cannot free itself. Once emerged the nymphs will eat the cast skin. Adulthood is reached for most species after several months and many molts. The lifespan of phasmatodea varies by species, but ranges from a few months to up to two years for some tropical varieties.
and resilience in climax forests
. By lowering the net production of early successional plants by consuming them and then augmenting the nutrients in the soil available to later successional plants through defecation
, the walking stick ensures that the tendency of early successional plants to swiftly immobilize soil nutrients in light-gaps does not stymie new substantial growth and the recycling of the tropical forest.
Phasmatodea is recognized as a defoliator that is injurious to forest and shade trees. D. violenscens, P. wilkinsoni and C. tessulatus in Australia, Diapheromera femorata in North America
and G. crouani in coconut plantations in the South Pacific
all occur in outbreaks of economic importance. Indeed, in the American South as well as in Michigan
and Wisconsin
, the walking stick is a significant problem in parks and recreation sites where it preys on the foliage of oak
s and other hardwood
s. Severe outbreaks of D. femorata have occurred in the Ouachita Mountains
of Arkansas
and Oklahoma
. The insects eat the entire leaf blade. In the event of heavy outbreaks, entire stands of trees can be completely ravaged. Continuous defoliation over several years often results in the death of the tree. Fortunately for control efforts, because the insects cannot fly, infestations are typically contained to a radius of a few hundred yards. Nevertheless, the damage incurred to parks in the region is often costly. Control efforts in the case of infestations have typically involved chemical pesticide
s. However, investigations have been made into natural enemies of phasmatodea such as birds and parasitic wasps (such as the cleptid wasp Myrmecomimesis).
. Phasmatodea is correctly formed, and is gaining in popularity. The term "Cheleutoptera" is now considered outdated.
Phasmatodea is sometimes considered related to other orders, including the Blattaria, Mantodea, Notoptera
and Dermaptera, but the affiliations are uncertain and the grouping (sometimes referred to as "Orthopteroidea") may be paraphyletic and hence invalid in the traditional circumscription. Phasmatodea was once considered a suborder of Orthoptera
, although most authors now consider it to be an order of its own. There are anatomical features that separate them as a monophyletic group from the Orthoptera. One is the instance among all species of Phasmatodea of a pair of exocrine glands inside the prothorax used for defense. Another is the presence of a specially formed sclerite called a vomer that allows the male to clasp the female during mating.
The order is divided into two, sometimes three suborders. The most common
division is into the suborder groups Anareolatae and Areolatae, which are distinguished
according to whether the insect has sunken areola, or circular areas, on the underside of the
apices of the middle and hind tibiae (Areolate) or not (Anareolate).
There are in excess of 3,000 described species, with many more yet to be described both in museum collections and in the wild.
. There is a large
effort in Australia to rear this species in captivity
. The best known of the stick insects is the Indian or Laboratory stick insect (Carausius morosus
). These insects grow to roughly 10 centimeters (3.9 in). They reproduce parthenogenically and males are unrecorded, although part male part female gynandromorph
s are relatively common.
it enhances crypsis by mimicking vegetation moving in the wind. However, the repetitive
swaying movements may be most important in allowing the insects to discriminate objects from
the background by relative motion. Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion to help them discern objects in the foreground.
Mating behavior in Phasmatodea is impressive because of the extraordinarily long duration of
pairings. A record among insects, the stick insect Necroscia sparaxes, found in India, is
sometimes coupled for 79 days at a time. It is not uncommon for this species to assume the
mating posture for days or weeks on end, and among some species (Diapheromera veliei Walsh
and D. Covilleae), pairing has been observed to last 3-136 hours in captivity.
Explanations for this behavior range from males guarding their mates against reproductive
competitors to the view that the pairings are a defensive alliance.
Instances of overt displays of aggression between males over mates would suggest that the
extended pairing behavior may have evolved to guard females against sperm competition
.
Fighting between competing males has been observed in the species D. veiliei and D. covilleae. During these encounters, the approach of a challenger causes the existing mate to manipulate the female's abdomen, which he has clasped by means of the clasping organ, or vomer, down upon itself to block the site of attachment. Occasionally the consort will strike out at the competitor with the mid femora, which are equipped with an enlarged and hooked spine in both sexes that has been observed to draw the blood of the opponent when they are flexed against the body to puncture the integument.
Usually a strong hold on the female's abdomen and blows to the intruder are enough to deter the unwanted competition, but occasionally the competitor has been observed to employ a sneaky tactic to inseminate the female. While the first mate is engaged in feeding and is forced to vacate the dorsal position, the intruder can clasp the female's abdomen and insert his genitalia. If he is discovered, the males will enter into combat wherein they lean backward, both clasped to the female's abdomen, and freely suspended, engage in rapid, sweeping blows with their forelegs in a manner similar to boxing
. Usually when the intruder gains attachment to the female's abdomen, these conflicts resolve in the displacement of the original mate.
Lengthy pairings have also been described in terms of a defensive alliance.
When cleaved together, the pair is more unwieldy for predators to handle. Also, the chemical defenses (secretions, reflex bleeding, regurgitation) of the individual stick insect are enhanced when two are paired together. Female survivorship of attacks by predators is significantly enhanced by pairing, largely because the dorsal position of the male functions well as a shield. This could indicate that manipulation by females is present: if females accept ejaculate at a slow rate, for instance, the males are forced to remain in copulo
for longer and the female's chances of survival are enhanced. Also, evolution could have simply favored males that remained attached to their females longer, since females are often less abundant than males and represent a valuable prize, so that for the lucky male even the sacrifice of his own life to preserve his offspring
with the female may be worth it.
Sexual dimorphism
in the species, where females are usually significantly larger than the males, may have evolved due to the fitness advantage accrued to males that can remain attached to the female, thereby blocking competitors, without severely impeding her movement.
Many stick insects are easy to care for in captivity. Almost 300 species have been reared in labs or as pets.
The most commonly kept, the Indian (or Laboratory) stick insect, Carausius morosus
, requires a tall (25+ cm) vivarium
(even a jar with a few holes punched in the top), some bramble
, ivy
, privet
and an atmosphere at room temperature. Indian stick insects are almost all female with only a few half-males (gynandromorphs), and these are not needed for reproduction. The females reproduce by parthenogenesis and seem content to live on their own. By the sixth molt the Indian stick insect will be sexually mature and can lay eggs.
Many of the other species of phasmids kept in captivity will feed on bramble. However, some are very specialist feeders and are therefore more difficult to rear. Beginners often make the mistake of thinking all species will feed on privet (the plant most commonly used to feed the Indian stick insect). In fact few species feed on privet. Most of the privet feeders on the Phasmid Study Group's culture list belong to the family Pseudophasmatidae
and are from South
America. Several of these will also feed on hebe. The few members of the family
Aschiphasmatidae that have been reared have to be fed on fuchsia
, willow herb, or evening primrose
. Some of the species in the subfamily Necrosciinae will only feed on hypericum
.
The optimal diet of phasmatodea in captivity during the winter months, or in colder climates, when/where tropical vegetation is scarce, is organic lettuce. A diet of carrots and spinach do not lead to the production of viable eggs and often leads to premature death.
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, whose members are variously known as stick insects (in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
), walking sticks or stick-bugs (in the United States and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
), phasmids, ghost insects and leaf insects (generally the family Phylliidae
Phylliidae
The family Phylliidae contains the extant true leaf insects or walking leaves, which include some of the most remarkable leaf mimics in the entire animal kingdom. They occur from South Asia through Southeast Asia to Australia...
). The ordinal name is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
φάσμα phasma, meaning an apparition or phantom, and refers to the resemblance of many species to sticks or leaves. Their natural camouflage can make them extremely difficult to spot. Phasmatodea can be found all over the world in warmer zones, especially the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
and subtropics
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
. The greatest diversity is found 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...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, followed by Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Phasmids also have a considerable presence in the continental United States, mainly in the Southeast
Southeastern United States
The Southeastern United States, colloquially referred to as the Southeast, is the eastern portion of the Southern United States. It is one of the most populous regions in the United States of America....
.
Anatomy
Phasmids can be relatively large, ranging from 1 inch to over a foot in length. Females of the genus PhobaeticusPhobaeticus
Phobaeticus is a genus of stick insects comprising over 25 species. It includes Phobaeticus chani, the longest known insect.The generic name of some species was formerly Pharnacia .-External links:* *...
are the world's longest insects, measuring up to 56.7 centimetres (22.3 in) in total length in the case of Phobaeticus chani
Phobaeticus chani
Phobaeticus chani or Chan's megastick is a species of stick insect. It is the longest insect in the world, with one specimen held in the Natural History Museum in London measuring . This measurement is however with the front legs fully extended...
, including the outstretched legs. Females of the species Heteropteryx dilatata
Heteropteryx dilatata
Heteropteryx dilatata is a large member of the Phasmatodea commonly kept in captivity. The most usual common name is the Malaysian or Malayan jungle nymph, often just shortened to jungle nymph.-Care in captivity:...
are the heaviest known phasmids, possibly weighing in excess of 65 grams.
Some have cylindrical stick-like bodies, while others have a flattened, leaflike shape. The thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
is long in the winged species, since it houses the flight muscles, but is typically much shorter in the wingless forms. Where present, the first pair of wings are narrow and cornified, while the hind wings are broad, with straight longitudinal veins and multiple cross-veins. The body is often further modified to resemble vegetation, with ridges resembling leaf veins, bark-like tubercles, and other forms of camouflage. A few species, such as Carausius morosus
Carausius morosus
Carausius morosus is a species of phasmid that is often kept by schools and individuals as pets. Culture stocks originate from an original collection from Tamil Nadu, India. Like the majority of the phasmatodea, they are nocturnal. Culture stocks are parthenogenetic females that can reproduce...
, are even able to change their pigmentation to match their surroundings. Many species are wingless, or have reduced wings. The mouthparts
Insect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...
project out from the head. Chewing mandibles are uniform across species. The legs are typically long and slender, and some species are capable of limb autotomy
Autotomy
Autotomy or self amputation is the act whereby an animal severs one or more of its own appendages, usually as a self-defense mechanism designed to elude a predator's grasp...
. They have long, slender 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....
that are as long or longer than the length of the body in some species.
All phasmids possess compound eyes, but ocelli are only found in some winged males. Phasmids have an impressive visual system that allow them to perceive significant detail even in dim conditions, which suits their typically nocturnal lifestyle. They are born equipped with tiny compound eyes with a limited number of facets. As the insect grows through successive molts, the number of facets is increased along with the number of photoreceptor cells in the eye. The sensitivity of the adult eye is at least tenfold that of the first instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
nymphs. As the eye grows more complex, the mechanisms to adapt to dark/light changes are also enhanced: eyes in dark conditions evidence less screening pigments, which would block light, than during the daytime, and changes in the width of the retinal layer to adapt to changes in available light are significantly more pronounced in adults. However, the larger size of the adult insect’s eyes makes them more prone to radiation damage. This explains why fully grown individuals are mostly nocturnal. Lessened sensitivity to light in the newly emerged insects helps them to escape from the leaf litter wherein they are hatched and move upward into the illuminated foliage. Young stick insects are diurnal feeders and will move around freely, expanding their foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
range.
Defense mechanisms
Phasmatodea species exhibit mechanisms for defense from predatorsPredation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
that both prevent an attack from happening in the first place (primary defense) and are deployed after an attack has been initiated (secondary defense).
The defense mechanism most readily identifiable with Phasmatodea is camouflage. Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as O. macklotti and Palophus centaurus) are covered in mossy or lichenous
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
outgrowths that supplement their disguise. Some species have the ability to change color as their surroundings shift (B. scabrinota, T. californica). In a further behavioral adaptation to supplement crypsis
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
, a number of species have been noted to perform a rocking motion where the body is swayed from side to side that is thought to reflect the movement of leaves or twigs swaying in the breeze. Another method by which stick insects avoid predation and resemble twigs is by feigning death (catalepsy
Catalepsy
Catalepsy is also a term used by hypnotists to refer to the state of making a hypnotised subject's arm, leg or back rigid. "Arm catalepsy" is often a pre-hypnotic test performed prior to an induction into a full trance.-Causes:...
), where the insect enters a motionless state that can be maintained for a long period. The nocturnal feeding habits of adults also aids Phasmatodea in remaining concealed from predators.
In a seemingly opposite method of defense, many species of Phasmatodea will seek to startle the encroaching predator by flashing bright colors that are normally hidden and making a loud noise. When disturbed on a branch or foliage, some species, while dropping to the undergrowth to escape, will open their wings momentarily during free fall to display bright colors that disappear when the insect lands. Others will maintain their display for up to 20 minutes, hoping to frighten the predator and convey the appearance of a larger size. Some accompany the visual display with noise made by rubbing together parts of the wings or antennae.
Some species, such as the young nymphs of E. tiaratum, have been observed to curl the abdomen upwards over the body and head to resemble ants or scorpions in an act of mimicry, another defense mechanism by which the insects avoid becoming prey.
When threatened, some phasmids that are equipped with femoral spines on the metathoracic
Metathorax
The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites are the metanotum , the metasternum , and the metapleuron on each side...
legs (O. martini, Eurycantha calcarata, Eurycantha horrida, D. veiliei, D. covilleae) respond by curling the abdomen upward and repeatedly swinging the legs together, grasping at the threat. If the menace is caught, the spines can draw blood and inflict considerable pain.
A number of species are equipped with a pair of glands at the anterior edge of the prothorax
Prothorax
The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites are the pronotum , the prosternum , and the propleuron on each side. The prothorax never bears wings in extant insects, though some fossil groups possessed...
that enable the insect to release defensive secretions, including chemical compounds of varying effect: from the production of distinct odors to the causing of a stinging, burning sensation in the eyes and mouth of a predator. The spray often contains pungent-smelling volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
metabolites, previously thought to be concentrated in the insect from its plant food sources. However, based on recent research it seems more likely that they manufacture their own chemical defense substances. Additionally, the chemistry of the defense spray from at least one species, Anisomorpha buprestoides
Anisomorpha buprestoides
Anisomorpha buprestoides is a stick insect which occurs throughout the southeastern United States.-Defense:...
, has been shown to vary based on their life stage and/or population. This chemical spray variation also corresponds with regionally specific color form populations in Florida who also have distinct behaviors. The spray from one species, Megacrania nigrosulfurea, is even used as a treatment for skin infections by a tribe in Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
because of its antibacterial constituents. Some species employ a shorter-range defensive secretion, where individuals bleed reflexively through the joints of their legs and the seams of the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
when bothered, allowing the blood (hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
), which contains distasteful additives, to discourage predators. Stick insects, like their distant relation the grasshopper, can also discharge the contents of their stomach through vomiting when harassed, a fluid that is considered inedible by some predators.
Life cycle
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
: she will either flick her egg to the ground by a movement of the ovipositor or her entire abdomen, carefully place the eggs in the axils of the host plant or bury them in small pits in the soil, or stick the eggs to a substrate
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
, usually a stem or leaf of the food plant. A single female lay from 100 to 1,200 eggs after mating, depending on the species. Most species of phasmid are parthenogenic, meaning that females lay eggs without needing to mate with males to produce offspring. However, some parthenogenic species retain the ability to mate and are bisexual depending on the presence and abundance of males. Eggs from virgin mothers are entirely female and exact copies of their mothers.
Phasmatodea eggs resemble seeds in shape and size, and have hard shells. They have a lid-like structure called an operculum
Operculum (animal)
An operculum is an anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal...
at the anterior pole, from which the nymph emerges during hatching. The eggs vary in the hatching period, from 13 to more than 70 days, with the average around 20-30 days. Some species, particularly those from temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
regions, undergo diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
, where development is delayed during the winter months. Diapause is affected by photoperiod on the egg-laying adults or can be genetically determined. Diapause is broken by exposure to the cold of winter, causing the eggs to hatch during the following spring. Among species of economic importance, diapause affects the development of 2-year cycles of outbreaks.
Many species' eggs bear a fatty knoblike capitulum that caps the operculum. This structure attracts ants because of its resemblance to the elaiosome
Elaiosome
Elaiosomes are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaiosomes to attract ants, which take the seed to their nest and feed the elaiosome to their larvae...
of some plant seeds that is a sought after food source for ant larvae, and usually contributes to ensuring seed dispersal by ants, a form of ant-plant mutualism called myrmecochory
Myrmecochory
Myrmecochory is seed dispersal by ants, an ecologically significant ant-plant interaction with worldwide distribution. Myrmecochorous plants produce seeds with elaiosomes, a term encompassing various external appendages or "food bodies" rich in lipids, amino acid, or other nutrients that are...
. The ants take the egg into their nest underground and can remove the capitulum to feed to their larvae without harming the phasmid embryo. There, the egg hatches and the young nymph, which initially resembles an ant (another instance of mimicry among phasmatodea), eventually emerges from the nest and climbs the nearest tree to safety in the foliage.
The Phasmatodea life cycle is hemimetabolous, proceeding through a series of several nymphal instars. The stick insect’s wings develop externally. As is the case with hatching, if the nymph is caught in the encasing of a rejected cast skin (or shell), it will likely die because it cannot free itself. Once emerged the nymphs will eat the cast skin. Adulthood is reached for most species after several months and many molts. The lifespan of phasmatodea varies by species, but ranges from a few months to up to two years for some tropical varieties.
Ecology
Phasmids are herbivorous, feeding mostly on the leaves of trees and shrubs, and a conspicuous component of many neotropical (South American) systems. Phasmatodea has been postulated as a dominant light-gap herbivore there. Its role in the forest ecosystem is considered important by many scientists who stress the significance of light gaps in maintaining successionEcological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
and resilience in climax forests
Climax vegetation
Climax vegetation is the vegetation which establishes itself on a given site for given climatic conditions in the absence of anthropic action after a long time ....
. By lowering the net production of early successional plants by consuming them and then augmenting the nutrients in the soil available to later successional plants through defecation
Defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...
, the walking stick ensures that the tendency of early successional plants to swiftly immobilize soil nutrients in light-gaps does not stymie new substantial growth and the recycling of the tropical forest.
Phasmatodea is recognized as a defoliator that is injurious to forest and shade trees. D. violenscens, P. wilkinsoni and C. tessulatus in Australia, Diapheromera femorata in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and G. crouani in coconut plantations in the South Pacific
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
all occur in outbreaks of economic importance. Indeed, in the American South as well as in Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
and Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
, the walking stick is a significant problem in parks and recreation sites where it preys on the foliage of oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
s and other hardwood
Hardwood
Hardwood is wood from angiosperm trees . It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.Hardwood contrasts with softwood...
s. Severe outbreaks of D. femorata have occurred in the Ouachita Mountains
Ouachita Mountains
The Ouachita Mountains are a mountain range in west central Arkansas and southeastern Oklahoma. The range's subterranean roots may extend as far as central Texas, or beyond it to the current location of the Marathon Uplift. Along with the Ozark Mountains, the Ouachita Mountains form the U.S...
of Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
and Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
. The insects eat the entire leaf blade. In the event of heavy outbreaks, entire stands of trees can be completely ravaged. Continuous defoliation over several years often results in the death of the tree. Fortunately for control efforts, because the insects cannot fly, infestations are typically contained to a radius of a few hundred yards. Nevertheless, the damage incurred to parks in the region is often costly. Control efforts in the case of infestations have typically involved chemical 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. However, investigations have been made into natural enemies of phasmatodea such as birds and parasitic wasps (such as the cleptid wasp Myrmecomimesis).
Taxonomy
The classification of the Phasmatodea is complex. There are many people, including amateur entomologists, studying the order, and revisions are commonplace. Furthermore, there is much confusion over the ordinal name. Phasmida is preferred by many authors even though it is incorrectly formedInternational Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
. Phasmatodea is correctly formed, and is gaining in popularity. The term "Cheleutoptera" is now considered outdated.
Phasmatodea is sometimes considered related to other orders, including the Blattaria, Mantodea, Notoptera
Notoptera
The insect order Notoptera, a group first proposed in 1915, has been largely unused since its original conception, but in the most recent classification of the lineage of insects that includes the Grylloblattodea and Mantophasmatodea, the name was resurrected and redefined so as to give a single...
and Dermaptera, but the affiliations are uncertain and the grouping (sometimes referred to as "Orthopteroidea") may be paraphyletic and hence invalid in the traditional circumscription. Phasmatodea was once considered a suborder of Orthoptera
Orthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
, although most authors now consider it to be an order of its own. There are anatomical features that separate them as a monophyletic group from the Orthoptera. One is the instance among all species of Phasmatodea of a pair of exocrine glands inside the prothorax used for defense. Another is the presence of a specially formed sclerite called a vomer that allows the male to clasp the female during mating.
The order is divided into two, sometimes three suborders. The most common
division is into the suborder groups Anareolatae and Areolatae, which are distinguished
according to whether the insect has sunken areola, or circular areas, on the underside of the
apices of the middle and hind tibiae (Areolate) or not (Anareolate).
There are in excess of 3,000 described species, with many more yet to be described both in museum collections and in the wild.
Notable species
One Australian species, the Lord Howe Island stick insect, is now listed as critically endangered. It was believed extinct until its rediscovery on the rock known as Ball's PyramidBall's Pyramid
Ball's Pyramid is an erosional remnant of a shield volcano and caldera that formed about 7 million years ago. Ball's Pyramid is southeast of Lord Howe Island in the Pacific Ocean. It is high, while measuring only in length and across, making it the tallest volcanic stack in the world...
. There is a large
effort in Australia to rear this species in captivity
Captivity (animal)
Animals that live under human care are in captivity. Captivity can be used as a generalizing term to describe the keeping of either domesticated animals or wild animals. This may include for example farms, private homes and zoos...
. The best known of the stick insects is the Indian or Laboratory stick insect (Carausius morosus
Carausius morosus
Carausius morosus is a species of phasmid that is often kept by schools and individuals as pets. Culture stocks originate from an original collection from Tamil Nadu, India. Like the majority of the phasmatodea, they are nocturnal. Culture stocks are parthenogenetic females that can reproduce...
). These insects grow to roughly 10 centimeters (3.9 in). They reproduce parthenogenically and males are unrecorded, although part male part female gynandromorph
Gynandromorph
A gynandromorph is an organism that contains both male and female characteristics. The term gynandromorph, from Greek "gyne" female and "andro" male, is mainly used in the field of Lepidopterology or entomology...
s are relatively common.
Behavior
Stick insects, like praying mantises, show rocking behavior in which the insect makes rhythmic, repetitive side-to-side movements. The common interpretation of this behavior's function is thatit enhances crypsis by mimicking vegetation moving in the wind. However, the repetitive
swaying movements may be most important in allowing the insects to discriminate objects from
the background by relative motion. Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion to help them discern objects in the foreground.
Mating behavior in Phasmatodea is impressive because of the extraordinarily long duration of
pairings. A record among insects, the stick insect Necroscia sparaxes, found in India, is
sometimes coupled for 79 days at a time. It is not uncommon for this species to assume the
mating posture for days or weeks on end, and among some species (Diapheromera veliei Walsh
and D. Covilleae), pairing has been observed to last 3-136 hours in captivity.
Explanations for this behavior range from males guarding their mates against reproductive
competitors to the view that the pairings are a defensive alliance.
Instances of overt displays of aggression between males over mates would suggest that the
extended pairing behavior may have evolved to guard females against sperm competition
Sperm competition
Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...
.
Fighting between competing males has been observed in the species D. veiliei and D. covilleae. During these encounters, the approach of a challenger causes the existing mate to manipulate the female's abdomen, which he has clasped by means of the clasping organ, or vomer, down upon itself to block the site of attachment. Occasionally the consort will strike out at the competitor with the mid femora, which are equipped with an enlarged and hooked spine in both sexes that has been observed to draw the blood of the opponent when they are flexed against the body to puncture the integument.
Usually a strong hold on the female's abdomen and blows to the intruder are enough to deter the unwanted competition, but occasionally the competitor has been observed to employ a sneaky tactic to inseminate the female. While the first mate is engaged in feeding and is forced to vacate the dorsal position, the intruder can clasp the female's abdomen and insert his genitalia. If he is discovered, the males will enter into combat wherein they lean backward, both clasped to the female's abdomen, and freely suspended, engage in rapid, sweeping blows with their forelegs in a manner similar to boxing
Boxing
Boxing, also called pugilism, is a combat sport in which two people fight each other using their fists. Boxing is supervised by a referee over a series of between one to three minute intervals called rounds...
. Usually when the intruder gains attachment to the female's abdomen, these conflicts resolve in the displacement of the original mate.
Lengthy pairings have also been described in terms of a defensive alliance.
When cleaved together, the pair is more unwieldy for predators to handle. Also, the chemical defenses (secretions, reflex bleeding, regurgitation) of the individual stick insect are enhanced when two are paired together. Female survivorship of attacks by predators is significantly enhanced by pairing, largely because the dorsal position of the male functions well as a shield. This could indicate that manipulation by females is present: if females accept ejaculate at a slow rate, for instance, the males are forced to remain in copulo
Sexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...
for longer and the female's chances of survival are enhanced. Also, evolution could have simply favored males that remained attached to their females longer, since females are often less abundant than males and represent a valuable prize, so that for the lucky male even the sacrifice of his own life to preserve his offspring
Offspring
In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...
with the female may be worth it.
Sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in the species, where females are usually significantly larger than the males, may have evolved due to the fitness advantage accrued to males that can remain attached to the female, thereby blocking competitors, without severely impeding her movement.
Stick insects as pets
The most commonly kept, the Indian (or Laboratory) stick insect, Carausius morosus
Carausius morosus
Carausius morosus is a species of phasmid that is often kept by schools and individuals as pets. Culture stocks originate from an original collection from Tamil Nadu, India. Like the majority of the phasmatodea, they are nocturnal. Culture stocks are parthenogenetic females that can reproduce...
, requires a tall (25+ cm) vivarium
Vivarium
A vivarium is a usually enclosed area for keeping and raising animals or plants for observation or research...
(even a jar with a few holes punched in the top), some bramble
Bramble
Brambles are thorny plants of the genus Rubus, in the rose family . Bramble fruit is the fruit of any such plant, including the blackberry and raspberry. The word comes from Germanic *bram-bezi, whence also German Brombeere , Dutch Braam and French framboise...
, ivy
Ivy
Ivy, plural ivies is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to western, central and southern Europe, Macaronesia, northwestern Africa and across central-southern Asia east to Japan and Taiwan.-Description:On level ground they...
, privet
Privet
Privet was originally the name for the European semi-evergreen shrub Ligustrum vulgare, and later also for the more reliably evergreen Ligustrum ovalifolium , used extensively for privacy hedging. It is often suggested that the name privet is related to private, but the OED states that there is no...
and an atmosphere at room temperature. Indian stick insects are almost all female with only a few half-males (gynandromorphs), and these are not needed for reproduction. The females reproduce by parthenogenesis and seem content to live on their own. By the sixth molt the Indian stick insect will be sexually mature and can lay eggs.
Many of the other species of phasmids kept in captivity will feed on bramble. However, some are very specialist feeders and are therefore more difficult to rear. Beginners often make the mistake of thinking all species will feed on privet (the plant most commonly used to feed the Indian stick insect). In fact few species feed on privet. Most of the privet feeders on the Phasmid Study Group's culture list belong to the family Pseudophasmatidae
Pseudophasmatidae
Pseudophasmatidae is a family of stick insect, commonly called the "striped walkingsticks".An important identifying characteristic is its mesothorax, which is never more than three times as long as the prothorax.Tribes and genera are as...
and are from South
America. Several of these will also feed on hebe. The few members of the family
Aschiphasmatidae that have been reared have to be fed on fuchsia
Fuchsia
Fuchsia is a genus of flowering plants that consists mostly of shrubs or small trees. The first, Fuchsia triphylla, was discovered on the Caribbean island of Hispaniola in 1703 by the French Minim monk and botanist, Charles Plumier...
, willow herb, or evening primrose
Evening Primrose
Evening Primrose is a musical with a book by James Goldman and lyrics and music by Stephen Sondheim. It is based on a John Collier short story published in the 1951 collection Fancies and Goodnights....
. Some of the species in the subfamily Necrosciinae will only feed on hypericum
Hypericum
Hypericum is a genus of about 400 species of flowering plants in the family Hypericaceae ....
.
The optimal diet of phasmatodea in captivity during the winter months, or in colder climates, when/where tropical vegetation is scarce, is organic lettuce. A diet of carrots and spinach do not lead to the production of viable eggs and often leads to premature death.