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southern black widow

southern black widow (Latrodectus mactans) [female]
Photo © Hank Guarisco

Features and Behaviors

The female southern black widow has a shiny, black body with red spots on the top side of the rounded abdomen. Usually there is a red, hourglass-shaped mark on the belly side of the abdomen. The male’s abdomen is flatter than that of the female and has red and white spots. The male is much smaller than the female. The female’s body length is slightly under one-half inch while that of the male is about one-fourth inch.

The southern black widow builds its web near the ground in secluded places or indoors in sheds and barns throughout Illinois. The web is an irregular network of threads with a funnel area for retreating from danger or bad weather. Insects trapped in the web are eaten as food. Mating occurs in May. After mating, the female sometimes kills and eats the male. If she doesn’t eat him, he dies soon anyway. The female produces a series of egg sacks, each with a nipplelike projection at the top. The female may live for about three years. The venom of the female is very toxic to humans, but humans are rarely bitten because this spider is shy and not aggressive. The venom is a neurotoxin that causes nerve cell functions to be blocked and nerve cells to be destroyed. Symptoms of a black widow bite include sharp pain starting at the bite location and spreading over the body within one-half hour, cramps, muscle spasms, muscle rigidity, sweating, dizziness, nausea and vomiting. An antivenin is available. Most bite victims recover fully.

Illinois Range


Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Family: Theridiidae

Illinois Status: common, native