Latrodectus mactans, the (
southern)
Black widow, is a species of spider in the genus
Latrodectus. They are well known for the distinctive black and red coloring of the female of the species and for the fact that she will occasionally eat her mate after reproduction. The highly venomous species is native to the United States of America. The female black widow's venom is particularly harmful to humans (males almost never bite humans). The injection of venom from these species is a comparatively dangerous or lethal bite.
Taxonomy
Latrodectus mactans was first described by
Johan Christian FabriciusJohan Christian Fabricius was a Danish entomologist and economist.Fabricius was born at Tønder in the duchy of Schleswig. He studied at the gymnasium at Altona and entered the University of Copenhagen in 1762...
in 1775, placing it in the genus
Aranea.
It is currently placed amongst the Theridiidae family of the order Araneae.
The species is closely related to
Latrodectus hesperusLatrodectus hesperus, the Western black widow spider or Western widow, is a highly venomous spider species found in western regions of the United States of America. The female's body is 14–16 millimeters in length and is black, often with an hourglass shaped red mark on the lower abdomen...
(western black widow) and
Latrodectus variolusLatrodectus variolus, the Northern black widow spider or Northern widow, is a highly venomous spider species of the Theridiidae family. The population is closely related to the Southern Black Widow, Latrodectus mactans, and the Western Black Widow, Latrodectus hesperus, of the...
(northern black widow). Members of the three species are often confused with the genus
SteatodaThe spider genus Steatoda, in the family Theridiidae, includes over 120 recognized species, distributed around the world ....
, the False Black Widows.
Prior to 1970, when the current taxonomic divisions for
North AmericaNorth America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...
n black widows were set forth by Kaston, all three varieties were classified as a single species,
L. mactans. As a result, there exist numerous references which claim that "black widow" (without any geographic modifier) applies to
L. mactans alone. Common usage of the term "black widow" makes no distinction between the three species.
Description
The mature female is around 1.5 in (38 mm) long and 0.25 in (6.4 mm) in diameter. She is shiny and black in color, with a red marking in the shape of an
hourglassAn hourglass, also known as a sandglass, sand timer, sand clock or egg timer, is a device for the measurement of time. It consists of two glass bulbs placed one above the other which are connected by a narrow tube. One of the bulbs is usually filled with fine sand which flows through the narrow...
on the ventral (under) side of her very rounded
abdomenIn 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...
. There is much variation in female size, particularly in egg-carrying (gravid) females. The abdomen of a gravid female can be more than 0.5 in (~1.25 cm) in diameter. Many female widows also have an orange or red patch just above the spinnerets on the top of the abdomen.
The male is either black, or closer to the appearance of the juveniles in color, and is much smaller with a body of less than 1/4 inch (< 0.75 cm).
Juveniles have a distinctly different appearance to the adults, the abdomen is grayish to black with white stripes running across it and is spotted with yellow and orange.
Range
The southern widow is primarily found in (and is indigenous to) the
southeastern United StatesThe US Southeast is the eastern portion of the Southern United States, but the Census Bureau does not provide a standard definition of a "Southeast" region of the United States, and organizations that need to subdivide the US are free to define a "Southeast" region to fit their needs...
, ranging from
FloridaFlorida is a state located in the southeastern region of the United States, bordering Alabama to the northwest and Georgia to the north. It was the 27th state admitted to the United States...
to
New YorkNew York is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous. The state is bordered by New Jersey and Pennsylvania to the south, and Connecticut, Massachusetts and Vermont to the east...
, and west to
TexasTexas is the second-largest U.S. state in both area and population, and the largest state in the contiguous United States.The name had wide usage among native Americans, meaning "friends" or "allies"...
,
OklahomaOklahoma is a state located in the South Central region of the United States of America. With an estimated 3,617,316 residents in 2007 and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
,
ArizonaThe State of Arizona is a state located in the southwestern region of the United States. The capital and largest city is Phoenix. The second largest city is Tucson, followed in size by the four Phoenix metropolitan area cities of Mesa, Glendale, Chandler, and Scottsdale.Arizona was the 48th and...
, and
NevadaNevada is a state located in the western region of the United States. The capital is Carson City and the largest city is Las Vegas. The state's nickname is Silver State, due to the large number of silver deposits that were discovered and mined there...
The northern black widow
(L. variolus) is found primarily in the
northeastern United StatesThe Northeastern United States is a region of the United States. According to the definition used by the United States Census Bureau, the Northeast region consists of nine states: the New England states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island and Connecticut; and the...
and southeastern
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
, though its ranges overlaps that of
L. mactans. In Canada, black widows range in the southern parts of British Columbia, Alberta, Manitoba and Ontario.
Latrodectus mactans, along with
Latrodectrus hesperus and
Latrodectus geometricusThe spider Latrodectus geometricus, commonly known as the brown widow, grey widow, brown button spider, or geometric button spider, is one of the widow spiders in the genus Latrodectus. As such, it is a "cousin" to the more famous black widow spider...
(the "brown widow spider"), is established in the Hawaiian Islands (USA). One pathway of entry into Hawaii for at least one of these black widow species is imported produce (which is also considered an important potential pathway for widow spiders elsewhere).
Reproduction
When a male is mature, he spins a sperm web, deposits semen on it, and charges his palpi with the sperm. Black widow spiders reproduce sexually when the male inserts his palpus into the female's spermathecal openings. The female deposits her eggs in a globular silken container in which they remain camouflaged and guarded. A female black widow spider can produce four to nine egg sacs in one summer, each containing about 100-400 eggs. Usually, eggs incubate for twenty to thirty days. Rarely do more than a hundred survive through this process. On average, thirty will survive through the first
moltingEcdysis is the moulting of the cuticula in arthropods and related groups . Since the cuticula of these animals is also the skeletal support of the body and is inelastic, it is shed during growth and a new, larger covering is formed...
, because of
cannibalismCannibalism is the act or practice of humans eating the flesh of other humans.The word can be extended into zoology to mean any species consuming members of its own kind, and used outside of biological fields in a metaphorical sense: "Cannibalization" refers to the reuse of parts or ideas, such as...
, lack of food, or lack of proper shelter. It takes two to four months for black widow spiders to mature enough to breed, however full maturation typically takes six to nine months. The females can live for up to five years, while a male's lifespan is much shorter. The female, on occasion, eats the male after mating.
Latrodectus mactans is the only black widow species for which this form of
sexual cannibalismSexual cannibalism is a special case of cannibalism in which a female organism kills and consumes a male of the same species before, during, or after copulation. Rarely, these roles are reversed...
has been observed in the wild. Lifespans depend upon environment, with shelter being the greatest determining factor and food the second greatest. Males that escape being consumed by the females can go on to fertilize other females. It is a widely held misconception that females eat males after every mating.
Prey
Black widow spiders typically prey on a variety of insects, but occasionally they do feed on woodlice, diplopods, chilopods and other arachnids. When the prey is entangled by the web,
Latrodectus mactans quickly comes out of its retreat, wraps the prey securely in its strong web, then bites and envenoms its prey. The venom takes about ten minutes to take effect; in the meantime, the prey is held tightly by the spider. When movements of the prey cease, digestive enzymes are released into the wound. The black widow spider then carries its prey back to its retreat before feeding.
Natural enemies
There are various parasites and predators of widow spiders in
North AmericaNorth America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...
, though apparently none of these have ever been evaluated in terms of augmentation programs for improved biocontrol. Parasites of the egg sacs include the flightless
scelionid waspThe Hymenopteran family Scelionidae is a very large cosmopolitan group of exclusively parasitoid wasps, mostly small , often black, often highly sculptured, with elbowed antennae that have an 9- or 10-segmented flagellum.They are generally idiobionts, attacking the eggs of many different types of...
Baeus latrodecti, and members of the
chloropid flyChloropidae is a family of flies commonly known as frit flies or grass flies. There are approximately 2000 described species in over 160 genera distributed worldwide. These are usually very small flies, yellow or black and appearing shiny due to the virtual absence of any hairs. The majority of the...
genus
PseudogauraxPseudogaurax is a genus of fly in the family Chloropidae.-References:**...
. Predators of the adult spiders include a few wasps, most notably the
blue mud dauberMud dauber is a name commonly applied to a number of wasps from either the family Sphecidae or Crabronidae that build their nests from mud...
,
Chalybion californicum, and the
spider waspWasps in the family Pompilidae are commonly called spider wasps . The family is cosmopolitan, with some 4,200 species in 4 subfamilies...
Tastiotenia festiva. Other species will occasionally and opportunistically take widows as prey, but the preceding all exhibit some significant specific preference for
Latrodectus.
Venom
Although these spiders are not especially large, their venom is extremely potent. Compared to many other species of spiders, their
cheliceraeThe chelicerae are mouth parts 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 not very large or powerful. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1.0 millimeters (about 0.4 in) long, long enough to inject the venom to a point where it can be harmful. The males, being much smaller, inject far less venom with smaller chelicerae. The actual amount injected, even by a mature female, is very small in physical volume. When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose (though it can produce the very unpleasant symptoms of
latrodectismLatrodectism is the clinical syndrome caused by the neurotoxic venom , that can be injected by the bite of any spider that is a member of the spider genus Latrodectus, in the family Theridiidae....
). Deaths in healthy adults from
Latrodectus bites are relatively rare in terms of the number of bites per thousand people. Sixty-three deaths were reported in the United States between 1950 and 1959. On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of their genus. Widow spiders have more potent venom than most spiders, and prior to the development of
antiveninAntivenom is a biological product used in the treatment of venomous bites or stings. Antivenom is created by injecting a small amount of the targeted venom into an animal such as a horse, sheep, goat, or rabbit; the subject animal will undergo an immune response to the venom, producing antibodies...
, 5% of reported bites resulted in fatalities. The venom can cause a swelling up to 15 cm.
Improvements in plumbing have greatly reduced the incidence of bites and fatalities in areas where
outdoor priviesAn outhouse is a type of toilet in a small structure separate from the main building which does not have a flush and is not attached to a sewer.- Terminology :...
have been replaced by
flush toiletA flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing...
s.
There are a number of active components in the venom:
- Latrotoxin
A latrotoxin is a high-molecular mass neurotoxin found in the venom of spiders of the genus Latrodectus . Latrotoxin are the main active components of the venom and are responsible for the symptoms of latrodectism....
s
- A number of smaller polypeptides - toxins interacting with cation channels which display spatial structure homology - which can affect the functioning of calcium, sodium, or potassium channels.
- Adenosine
Adenosine is a nucleoside composed of a molecule of adenine attached to a ribose sugar molecule moiety via a β-N
9-glycosidic bond....
- Guanosine
Guanosine is a nucleoside comprising guanine attached to a ribose ring via a β-N
9-glycosidic bond.Guanosine can be phosphorylated to become GMP , cGMP , GDP and GTP .When guanine is attached to a deoxyribose ring, it is known as a...
- Inosine
Inosine is a nucleoside that is formed when hypoxanthine is attached to a ribose ring via a β-N
9-glycosidic bond....
- 2,4,6-trihydroxypurine.
The venom is
neurotoxicA neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels.Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
.
External links