The female southern black widow is normally a shiny jet-black spider 5/16 to 1/2 in body length. With legs extended, the female measures about 63/64 to 1 1/4 inch long. The male, which is black and has white underbody markings with red spots, is only 5/32 to 15/64 inches long (15/32 to 45/64 inches including its legs). The female has the well known reddish hourglass marking on the underside of her abdomen.

Black widows can be found under stones, in stumps or woodpiles, in vacant rodent holes, in the dark corners of barns and garages, and in outdoor privies and other undisturbed cavities. Their webs are skimpy and disorganized. Males are often killed and eaten by the females shortly after mating, thus the origin of the name "widow." A female may live for a year or more and produce up to 9 half-inch-diameter egg cases (called "cocoons"), each containing 200 to 800 eggs. Eggs hatch in about 8 days, but the young spiders remain in the egg case for about 9 more days, molting once during that time. They then disperse, traveling on thin silken threads through a process known as "ballooning." The female stands guard over the eggs during the summer months-when the majority of widow bites occur.

Medical Importance: The bite of female black widows is, at first, relatively painless. Pain will be felt about 1 to 2 hours later, and occasionally the patient may experience a tingling along the nerve routes or down the spine. There is almost no swelling at the site of the bite. However, the site will typically exhibit 2 red fang marks and may be surrounded by a rash. Black widow venom is principally neurotoxic. Generalized body symptoms, which develop within 1 to 3 hours, may include any of the following: nausea, chills, slight fever, rise in blood pressure, retention of urine, burning sensation of the skin, fatigue, motor disturbances, breathing difficulty, constipation, and muscle aches, particularly in the abdomen. These symptoms usually disappear after 4 days. Death does not normally occur, except in the elderly or very young.