Black Widow Spiders

Genus Latrodectus

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black widow spider
Black Widow
(Latrodectus mactans)

spider fang
Magnified spider fang. The hairy region below is the proximal segment of the chelicera. The fang is hollow, allowing injection of venom. More about spider anatomy >>.

spider fang
Worldwide distribution of genus Latrodectus
(Enlarged image)

Black widow spiders — spiders of the genus Latrodectus — account for more deaths worldwide than any other type of spider. Latrodectid spiders are small and therefore harder to detect than larger spiders, and their venom is far more potent. The poison is a neurotoxin known as latrotoxin. Though potent, it is much slower-acting than the neurotoxin of the golden poison frog, which can cause immediate death.

Compared with those of most other spiders, the fangs of black widows are small—in females, only about 1 mm (0.04 in) long. But they are still long enough to administer a dangerous bite. Males, which have smaller poison glands and fangs than females, inject much less venom and less deeply. Even in the case of a female, the volume injected is only .02-.03 mg, not enough, in most cases, to kill an adult human being.

In Latrodectus mactans (see picture, above right), which is found in North and South America, females are a shiny, coal black, 10 mm long, and have round, nearly spherical, abdomens. Males are only about half as long and have elongated abdomens. Usually the ventral side of the female’s abdomen has a bright red, usually hourglass-shaped, marking (but this is not always present). A male’s abdomen has four pairs of red-and-white stripes on its sides.

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