Black widow spiders are found in protected places, such as under rocks, wooden boards and in dense plant growth. They frequently nest in electrical, water and telephone equipment boxes outdoors. Around homes, these spiders may be found in crawlspaces, beneath appliances, usually in corners that are dark and damp. The female produces an egg sac containing 250-750 eggs that hatch in two to four weeks, depending upon temperature. The spiders spin a web that is used to ensnare prey, mostly insects, but sometimes other spiders as well. The trapped victim is bitten, then injected with venom to paralyze it.

Black widow spider venom affects the nervous system. Because the bite itself is relatively mild, some people may not even realize immediately that they were bitten. The venom causes pain in the lymph nodes. Other symptoms of a severe bite include nausea, elevated blood pressure, sweating, tremors and increased white blood cell counts. The wound may appear as a bluish red spot, surrounded by a whitish area. Both male and female spiders bite, but adult females produce the most severe bites. An antivenom serum is available through a physician, but it must be administered soon as possible after the bite occurs.