Latrodectus is a genus of
spider, in the family Theridiidae, which contains 32 recognized species. The common name, widow spiders, is sometimes applied to members of the genus due to a behavior seen in some species in which the female eats the male after mating.
The black widow spider is perhaps the best-known member of the genus. Its bite is dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism, both named for the genus. The female black widow has unusually large venom glands and its bite is particularly harmful to humans however, Latrodectus bites rarely kill humans if proper medical treatment is provided.
The prevalence of sexual cannibalism in Latrodectus females has inspired the common name "black widow spider". The females frequently eat their male partners after mating. The female's venom is at least three times more potent than that of the males, making a male's self-defense bite ineffective. Research at the University of Hamburg in Germany suggests this ultimate sacrifice strategy has evolved to promote the survival odds of the offspring.
In common with other members of the Theridiidae family, the widow
spiders construct a web of irregular, tangled, sticky silken fibers. The spider very frequently hangs upside down near the center of its web and waits for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to bite it and wrap it in silk. If the spider perceives a threat, it will quickly let itself down to the ground on a safety line of silk.
As other web-weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats. While some species are more aggressive, most are not; many injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched.
Some bites are thought to result from a spider mistaking a finger thrust into its web for its normal prey,or in cases where a female is protecting an egg sac, but ordinarily intrusion by any large creature will cause these spiders to flee.