Black Widow Spider

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 black widow is capable of inflicting a potentially dangerous bite; the wandering and seldom-seen male is harmless.

This timid arachnid often flees from disturbance but will bite if consistently provoked. 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.

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 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.
Distribution in Missouri: 
Both species occur statewide, although L. mactans is more common in southern countries.
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: 
Black widow bites are serious and should receive medical attention. Though you will probably want to kill widows where they can easily come in contact with people and pets, we encourage you to tolerate them in nature. They are not aggressive. Their first instinct is to flee.
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 daubers (wasps) prefer to hunt immature black widows and provision their nests with them.