Department of Entomology
Entomological Notes

Steatoda grossa

Steatoda grossa , one of at least eight Steatoda species occurring in the United States, is found along the coastal states of the Atlantic, Gulf, and Pacific regions. In the southern and western states, it is a common spider in homes and other structures, where it makes an irregular web (a trait shared by most comb-footed spiders) and is reported to capture and prey upon other spiders, including the true black widow spiders. Female Steatoda spiders have been reported to live for up to six years (males live for a year to a year and a half), producing numerous offspring.

Description

Similar to the true black widow, the false black widow female is 6 to 10.5 millimeters in length, but it lacks the red hourglass pattern on the underside of the abdomen, which is more oval in shape than that of the true black widow. In most specimens, the abdomen has a purplish-brown to black color with light, pale yellow to grayish markings. In many specimens, these markings may be faded and difficult to see. The cephalothorax is a red-brown color with slightly darker legs.

Life History

These spiders mate in the spring, and the females can produce three or more egg sacs or cocoons from May through July. Each sac can contain 200 or more cream-colored eggs. Although the males can live for up to 18 months, they die shortly after mating. All stages of the immature spiders can be found in human-made structures throughout the year, as can the adults. Outside, these spiders can be found on low-growing foliage, under bark, in rock crevices, and under bridges.

A closely related species, S. borealis, is similar in shape and coloration but is slightly smaller. This spider is more common in the northern states (Pennsylvania included) and can be found in dwellings throughout the year.

Medical Importance

These spiders are capable of biting but produce symptoms that are much less severe than those of a true black widow bite. There are documented cases of Steatoda bites leading to blistering at the site of the bite and to a general malaise lasting for several days. Care should be taken in diagnosing a black widow bite and in the administration of widow antivenom in the case of Steatoda bites. In all instances, it is advisable to submit the specimen to an entomologist for verification of the species.

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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