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Black Widow Spider

Updated on May 05, 2010

The Black Widow Spider is the common name for a group of poisonous spiders of the genus Latrodectus. They are found throughout the tropics as well as in many areas of the Northern and Southern hemispheres. They occur in a large number of habitats, usually near human dwellings or in cultivated areas. Their name is derived from the erroneous belief that the female invariably kills the male after mating.

Black widows are medium-sized spiders. Their bodies are about 1/2 inch (1.2 cm) long and they have shiny, black, globular abdomens, usually marked with bright red, yellow, or white. Two species are common in the United States. One is the southern black widow, the female of which has a red hourglass marking on the underside of her abdomen. The other, the northern black widow, has a row of red spots down the middle of the upper surface of its abdomen and two crosswise red bars on the undersurface.

Both these species spin irregular webs of very tough silk. They locate their webs in protected areas, usually on or near the ground, in dark corners or crevices, but seldom in human dwellings. The females are nocturnal in habit and timid. The males, which are smaller than the females, often wander in search of females during the brief mating season.

Only female black widows bite humans, and then only when disturbed. Their venom affects the victim's nervous system. The venoms of all species are protein in nature and very similar; thus an antivenin prepared against one venom is effective against all others. Some people are little affected by the venom, but others may have a severe response. The first reaction is acute local pain, which may be followed by localized muscular cramps, abdominal pains, weakness, and tremor. In extreme cases, nausea, vomiting, faintness, dizziness, and respiratory difficulties follow. The reaction depends on the physical condition and age of the victim and the location of the bite. Children are more seriously affected than adults.

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