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BackgroundLatrodectus mactans, the black widow, is the largest and most familiar member of the spider family Therididae, the cobweb weavers. The black widow's reputation as one of the most venomous terrestrial creatures, while accurate on the whole, tends to exaggerate the dangers presented by potential contact. Black widows generally are not aggressive unless confined or bothered, and the amount of venom a female injects is minute (the males are harmless). However, the venom's concentration is 15 times more toxic than an equal weight of prairie rattlesnake venom, and bites require immediate medical attention.
Mature black widows have glossy, jet black, rounded abdomens with a red hourglass-shaped ventral marking. Most adult females reach 1 ½ inches in size, including the legs, while many males achieve less than half this size, and tend to be more brown than black. The male black widow's body is smaller and its legs are longer than the female's. The black widow occurs throughout the United States, including the deserts of the Southwest, and thrives in many parts of the world to latitudes of 45 degrees North and South. The spider weaves its chaotic, coarse silk web in dark, sheltered outdoor areas such as woodpiles, garages or sheds, or under rocks and in tree cavities. Life CycleFemale black widows commonly lay about 400 (occasionally up to 900) eggs in oval, papery sacs, about ½ inch long. A single female can produce nine egg sacs in a summer. Eggs incubate for 20-30 days, after which the spiderlings hatch; however, more than 12 rarely survive this process, due to cannibalism.
Black widows mature in two to four months. At first the young appear white or yellowish, but with each molt their coloration darkens. Until maturity both sexes resemble the male and are harmless to humans. Females usually mature within 90 days, and live for another 180 days, while males usually mature about 70 days and live only about a month longer. The female black widow's notorious habit of eating the male after mating is the rule, but there are exceptions if the female is already well fed, and some males do escape to mate again. Females are nocturnal, shy and rarely leave their web, from which they hang, belly upward. Males and females feed on insects and other arthropods and are preyed upon by mud-dauber wasps. Once BittenThe black widow's bite may be felt only as a pin prick, during which the spider's fangs inject a minute amount of highly toxic venom under the skin. The severity of the victim's reaction depends on his or her age and health, and on the area of the body that is bitten. Local swelling and redness at the site may be followed in one to three hours by intense spasmodic pain, which can travel throughout the affected limbs and body, settling in the abdomen and back, and last 48 hours or longer. Elderly patients or young children run a higher risk of severe reactions, but it is rare for bites to result in death. Other symptoms can include nausea and profuse perspiration. If left untreated, tremors, convulsions and unconsciousness may result. If you are bitten by a black widow, contact your physician, hospital or poison center immediately and follow their instructions. Collect the spider if possible for identification. Your physician may administer an antivenom treatment and calcium gluconate to alleviate pain, and will probably treat the site with antiseptic to prevent infection. If you have a heart condition or are otherwise vulnerable, you may require a hospital stay until symptoms subside. Usually bite victims recover fully within two to five days.
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