The black widow, a relatively uncommon spider in the Kansas City area, lives in undisturbed locations under trash, litter, boards and rocks. Little-used buildings are often infested, along with crawl spaces, cellars and basements. 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.
Black widow spiders are shy and nocturnal. This timid arachnid often flees from disturbance but will bite if consistently provoked. Only the sedentary female black widow is capable of inflicting a potentially dangerous bite; the smaller, wandering and seldom-seen male is harmless. Bites usually occur when humans come into direct contact with the web or when the spider is unknowingly pinned against their skin.
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.
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. Females are about 3/8 inch (not counting legs); males grow to less than half this size.
Like most other spiders, black widow 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. In the Kansas City area all adults are killed by the first freezes; only the egg cases overwinter.