Department of Entomology
Entomological Notes

Latrodectus mactans

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.

Description

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 2006

References

Baerg, W. J. 1936. The Black Widow. Ark. Agr. Expt. Sta. Bul. 325. 34 pp.

Baerg, W. J. 1959. The Black Widow and Five Other Venomous Spiders in the United States. Ark. Agr. Expt. Sta. Bul. 608. 43 pp.

Breene, R. G., et al. 2003. Common Names of Arachnids. 5th ed. The American Arachnological Society Committee on Common Names of Arachnids. 42 pp.

Gertsch, W. J., and F. Ennik. 1983. “The spider genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae).” Bul Amer Mus. Nat. Hist. 175: 24–360.

Herms, W. B., and M. T. James. 1961. Medical Entomology. 5th ed. The MacMillan Company, New York. 616 pp.

Kaston, B. J. 1948. “Spiders of Connecticut.” Conn. State Geol. Nat. Hist. Survey. Bull. 70. 874 pp.

Kaston, B. J. 1972. How to Know the Spiders. 3rd. ed. Wm. C. Brown Company, Dubuque, Iowa. 272 pp.

Levi, H. W. 1959. “The Spider Genus Latrodectus (Araneae, Theridiidae). Trans. Amer. Microscopical Soc. Vol. LXXVIII (1): 7–43.

Long, D., R. Snetsinger, and K. F. Helm. 1995. “Localized Pruritic Rash Due to Recurrent Spider Bites.” J. Geriatr. Dermatol. 3(6): 186–190.

Vetter, R. S., and P. Kirk Visscher. 1998. “Bites and Stings of Medically Important Venomous Arthropods.” International. J. Derm. 37: 481–496.

Vetter, R. S. et al. 2006. “Verified Bites By Yellow Sac Spiders (Genus Cheiracanthium) in the United States and Australia: Where Is The Necrosis?” Amer. J. Trop. Med. Hyg., 74(6) 1,043–1,048.

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Entomological Notes are intended to serve as a quick reference guide and should not be used as a substitute for product label information. Although every attempt is made to produce Entomological Notes that are complete, timely, and accurate, the pesticide user bears the responsibility of consulting the pesticide label and adhering to those directions.

Issued in furtherance of Cooperative Extension Works, Acts of Congress May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and the Pennsylvania Legislature. D. Jackson, Director of Cooperative Extension, The Pennsylvania State University.

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