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Black Widow Spiders

Black Widow Spider

Latrodectus mactans and Latrodectus variolus
Family: 
Theridiidae (comb-footed spiders) in the order Araneae (spiders)
Description: 

The glossy, black-bodied female widows have distinctive red spots on the underside of their abdomens. In L. mactans this spot often is shaped like an hourglass; in L. variolus it is not. Faint red or white spots may also appear on top of the abdomen, as they do in males. Only the sedentary female is capable of inflicting a potentially dangerous bite; the smaller, wandering, and seldom-seen male is harmless. This spider is timid and usually flees when disturbed, but it will bite if consistently provoked.

Size: 
Length: females to about 3/8 inch (not counting legs); males grow to less than half this size.
Habitat and conservation: 
The black widow most often makes its irregularly shaped, rather tangled web under flat rocks, logs, along embankments, near foundations, or in outbuildings. The web has a tiny funnel into which the spider can retreat if bothered. L. variolus makes its web in open woods.
Foods: 
The black widow's prey includes flying and climbing insects that become entangled in its web. They have also been known to capture and kill small vertebrates, such as lizards and small snakes. Remember that nearly every species of spider uses a venomous bite to subdue its prey. There are only a few kinds, such as the black widow and brown recluse in our state, whose venom is medically significant.
Distribution in Missouri: 
Both species occur statewide, although L. mactans is more common in southern counties.
Status: 
Black widow bites are serious and should receive medical attention. A black widow spider bite often results in delayed pain at the wound site. Severe abdominal cramps, muscle tightness or soreness, headache, nausea, and sweating usually follow. Swelling may be noticed in the hands, feet, or eyelids, but usually not at the bite site. Discomfort can last several days and may be relieved through medical treatment. It is unusual for a widow bite to cause death.
Life cycle: 
Like most other spiders, eggs hatch in spring and young spiderlings disperse and begin the process of growing up. Females build webs to catch prey; males do not. Often the male is killed and eaten by the female directly after mating, a habit that gave these spiders their common name. Scientists have shown that the males, having done their job of fertilizing, feed their future families through this sacrifice. All adults are killed by the first freezes, and egg cases overwinter.
Human connections: 
You will probably want to kill widows where they can easily come in contact with people and pets, but please tolerate them in nature. They’re not aggressive and usually try to flee. Biotechnologists are studying the chemistry of black widow silk because of its remarkable strength and flexibility.
Ecosystem connections: 
Black widows, like other web-building spiders, control insect populations. Despite their ferocious stereotype, they are preyed upon by numerous other creatures. In fact, blue mud dauber wasps prefer to hunt immature black widows and provision their nests with them.
Shortened URL
http://mdc.mo.gov/node/6495