Black Widows: Facts & Information

A western black widow, <em>Latrodectus Hesperus</em>. One of the few species harmful to people in North America, a black widow often features a red hourglass shape on its underside.
A western black widow, Latrodectus Hesperus. One of the few species harmful to people in North America, a black widow often features a red hourglass shape on its underside.
Credit: © AMNH\R. Mickens

The black widow is a species of spider that is known for the females’ unique appearance and venomous bite. It has a shiny black body with red markings, and its venom is reported to be 15 times stronger than a rattlesnake's.

Black widows are found in temperate regions throughout the world, including the United States, Southern Europe and Asia, Australia, Africa, and much of South America. They are considered the most venomous spider in North America. In the United States, they exist primarily in the South and West. They are usually found in outdoor structures like fences, rock piles, sheds and outdoor furniture. In cold weather they may enter buildings.

Black widows (Latrodectus mactans) belong to a group of spiders commonly called cobweb spiders, “comb-footed,” or “tangle-web” spiders. These spiders build irregular, funnel-like webs of sticky silk. Female cobweb spiders are larger than males. There are three types of spiders in genus Latrodectus that are found in the United States and all go by the name “black widow spider.” These are eastern, northern, and western black widows, and all have similar appearances.

Female spiders can live up to three years. Males typically live for one or two months. They are primarily solitary, with the exception of late spring when mating occurs.

Black widow appearance

Male and female black widows look different. The female has a shiny black body with a globular abdomen. It has a blood-red (or occasionally orange-yellow) hourglass marking. She is about 1.5 inches long. The male is about half the size of the female. He is lighter in color with red or pink spots on his back.

Black widows’ legs are coated in an oily substance that prevents them from being caught in their own webs.

Black widow food

The black widow spider eats other arachnids and insects, which get caught in the web. The female spider hangs upside down from her web as she waits for her prey. In this pose, her bright markings are a visible warning to potential predators.

After the prey is ensnared in the web, the black widow uses its “comb-feet” to wrap the prey in silk. Then, the black widow punctures its prey with its fangs and injects digestive enzymes that liquify the corpse. The spider then sucks up the fluid.

A black widow spider spinning egg case silk.
Credit: Biology Department of the University of California, Riverside.

Black widow mating

The black widow gets its name from its bloody courtship ritual. After mating, the female often kills and eats the male, explaining the males’ short lifespans. The female then creates papery egg sacs that contain around 200 eggs each. The eggs hatch after about 30 days. The baby spiders are cannibalistic and few survive the three-month development to adulthood.

Black widow's bite

Black widows are highly poisonous; fortunately, they bite humans only when disturbed. Contrary to popular belief, most victims do not suffer serious damage. The black widow bite can occasionally be fatal, however, with small children, the elderly, or the physically infirm at the highest risk. If bitten, one should seek emergency medical attention immediately.

The black widow’s bite feels like a pinprick to most people, though some may not feel it at all. Initial symptoms may include minor swelling, redness, and a target-shaped lesion. After 15 to 60 minutes, dull muscle pain will spread from the bite-site to the entire body. Those with upper-body bites experience the most pain in their chests; those with lower-body bites experience it in their abdomens.

Common symptoms include muscle aches and weakness, nausea, headache, increased salivation and sweating, and difficulty breathing. There may be severe cramping or rigidity in the abdomen.

Pain may last for 8 to 12 hours and the other symptoms may continue for several days. Black widow antivenom is available to help minimize damage.

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