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Southern Black Widow Spider

Latrodectus mactans

Southern black widow spider

The widow spiders, genus Latrodectus, are found worldwide in the warmer regions of most continents. The taxonomy of these spiders is a challenge to scientists and has resulted in claims of few (six) to many (twenty-eight) distinct species. In the United States, there are probably five species. They are the southern black widow, L. mactans; northern black widow, L. variolus; western black widow, L. hesperus; brown widow, L. geometricus; and the red widow, L. bishopi.

The southern black widow, L. mactans, is found in Pennsylvania. It is probable that the northern black widow, L. variolus, is also present. Occasionally, the brown and the red widow spiders are introduced on potted plants from southern Florida.


The female southern black widow is normally a shiny, jet-black spider 8 to 13 millimeters in body length. With legs extended, the female measures about 25 to 35 millimeters long. The male, which is black and has white underbody markings with red spots, is only 4 to 6 millimeters long (12 to 18 millimeters including its legs). The female has the well-known reddish hourglass marking on the underside of her abdomen.

Life History

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 nine 0.5-inch-diameter egg cases (called “cocoons”), each containing 200 to 800 eggs. Eggs hatch in about eight days, but the young spiders remain in the egg case for about nine 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 one to two 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 two red fang marks and may be surrounded by a rash or erythema.

Black widow venom is principally neurotoxic. Generalized body symptoms, which develop within one to three 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 four days. Death does not normally occur, except in the elderly or very young.

Treatment typically includes the use of calcium gluconate (to reduce muscle cramps), Latrodectus antivenom, and diphenhydramine hypochloride (Benadryl®) to counteract allergic reactions to the antivenom. Additional treatments include antispasmatic medications and analgesics.

Authored by: Steve Jacobs, Sr. Extension Associate

March 2002 Revised 2015

This publication is available in alternative media on request.


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