Black widow spider

Black widow spider

name = Black widow

image_width = 211px
regnum = Animalia
phylum = Arthropoda
classis = Arachnida
ordo = Araneae
suborder: Labidognatha
familia = Theridiidae
genus = "Latrodectus"
subdivision_ranks = Species
subdivision = "L. mactans" Fabricius, 1775 "L. hesperus" Chamberlin & Ivie, 1935 "L. variolus" Walckenaer, 1837
The black widow spider is a group of spiders which includes the southern black widow ("Latrodectus mactans"), the northern black widow ("Latrodectus variolus"), and the western black widow ("Latrodectus hesperus"). As the name indicates, the southern widow is primarily found in (and is indigenous to) the southeastern United States, ranging from Florida to New York, and west to Texas, Oklahoma and Arizona, where they run particularly rampant. The northern black widow is found primarily in the northeastern United States and southeastern Canada, though its ranges overlap that of "L. mactans" quite a bit. The western widow is found in the western United States, as well as in southwestern Canada and much of Mexico. Black widows range in the southern parts of British Columbia, Alberta, Manitoba and Ontario - but only on the Bruce Peninsula. ["Black widows in Ontario? Absolutely, but only on the Bruce Penninsula." - John Acorn, "Bugs of Ontario", page 147] They are often confused with the False Black Widows.

Prior to 1970, when the current taxonomic divisions for North American black widows were set forth by Kaston [cite journal|author=Kaston, B. J.|date=1970|title=Comparative biology of American black widow spiders
journal=Transactions of the San Diego Society of Natural History
] , 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. Since common usage of the term "black widow" makes no distinction between the three species (and many people are unaware of the differences between them), and because the three species have much in common, this article treats all three species of black widow equally. Except where otherwise indicated, the remainder of the article applies to all three of the above species.

Black widow spiders typically prey on a variety of insects, but occasionally they do feed upon woodlice, diplopods, chilopods and other arachnids. [ [ Latrodetus Mactans] McCorkle, Matthew. October 17 2002.] When the prey is entangled by the web, "L. 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. [Foelix, R. (1982). "Biology of Spiders", pp. 162-163. Harvard University, U.S.]


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 molting, because of cannibalism, 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. "L. mactans" is the only black widow species for which this form of sexual cannibalism has been observed in the wild. Lifespans depend upon environment, with shelter being the greatest determining factor and food the second greatest.Jones, Susan C. (2000). [ Black Widow Spider Fact Sheet.] Ohio State University, U.S.] Males that escape being consumed by the females can go on to fertilize other females [cite journal|author= Breene, R . G . and M. H. Sweet|date=1985|title=Evidence of insemination of multiple females by the male black widow spider, Latrodectus mactans (Araneae, Theridiidae)| journal=The Journal of Arachnology| volume=13|issue=3|pages=331–335 [ PDF] ] . This is a general misconception, as the name seems to suggest that the males are invariably consumed after mating.

Natural enemies

There are various parasites and predators of widow spiders in North America, 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 wasp "Baeus latrodecti", and members of the chloropid fly genus "Pseudogaurax". Predators of the adult spiders include a few wasps, most notably the blue mud dauber, "Chalybion californicum", and the spider wasp "Tastiotenia festiva". Other species will occasionally and opportunistically take widows as prey, but the preceding all exhibit some significant specific preference for "Latrodectus".

Introduced range

There have been incidents in Sweden and Denmark with invasive black widow spiders being found in cars imported from the southern U.S. [ [ The Local - Black widow spider bites Swede after Atlantic voyage ] ] [ [ Giftig edderkop ynglede i garage i Ølstykke - ] ] and according to widely published information dated September 12, 2008, from Naturhistoriska Riksmuseet (The Swedish Museum of Natural History) in Stockholm the black widow spider has established itself in Sweden. [] The Swedish climate is suitable for black widow spiders and Bert Gustavsson, assistant curator at Naturhistoriska riksmuseet expects that the black widow spider will become a permanent part of the Swedish fauna now that the species have become established. [] The climate will likely allow the black widow spider to establish itself in large parts of Sweden, although this is rejected by Nikolaj Scharff, an expert in spiders from the Danish Zoological Museum. [ Svensk "svart änka" er en and] .


Although their venom is extremely potent (it is also reported to be much more potent than the venom of cobras and coral snakes), these spiders are not especially large. Compared to many other species of spiders, their chelicerae 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 .04 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 latrodectism). 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 [Miller T. Latrodectism: bite of the black widow spider. American family physician 1992; 45:181-187 .] . 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 antivenin, 5% [Bettini S. Epidemiology of latrodectism. Toxicon 1964; 2:93-101.] 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 privies have been replaced by flush toilets.

There are a number of active components in the venom:
* 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
* Guanosine
* Inosine
* 2,4,6-trihydroxypurine.

The venom is neurotoxic.Jones, Susan C. (2000). [ Black Widow Spider Fact Sheet.] Ohio State University, U.S.]


External links

* [ Latrodectus Mactans on Pterodattilo]
* [ Virginia Cooperative Extension: widow spiders]
* [ University of Washington Burke Museum spider myths]
* [ Bites and stings of medically important venomous spiders - UCR]
* [ Pictures of "L. mactans"] (free for noncommercial use)
* [ Western black widow]

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