Department of Entomology
Entomological Notes

Loxosceles reclusa and other Loxosceles species

Eleven species of Loxosceles are indigenous to the continental United States, four of which are known to be harmful to humans. Brown recluse spiders are established in 15 states: Alabama, Arkansas, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Ohio, Oklahoma, Tennessee, and Texas. In addition, isolated occurrences have been reported in Arizona, California, the District of Columbia, Florida, North Carolina, New Jersey, Pennsylvania, Washington, and Wyoming. Brown recluse spiders are rarely encountered in Pennsylvania, but they may be transported in boxes and similar items from a locale where the spiders normally occur.

A closely related species that is believed to have been introduced from southern Europe, Loxosceles rufescens , the Mediterranean recluse, has become established in the steam tunnels of Penn State and in other locations in the Northeast. These spiders are not known to have bitten any employees or students, despite their long sojourn in the Penn State steam tunnels. The bites of these spiders do not produce the severe reactions typically associated with the brown recluse spider.

Description

These spiders are chocolate brown in color, and their bodies are about 9 millimeters in length with long legs. They have three pairs of eyes, arranged in a triad, and have a violin-shaped marking on the cephalothorax. The body of the “violin” is near the eyes and the neck of the “violin” extends backward, ending before the abdomen. Males are similar to females in appearance.

Life History

After mating in June or July, the female will deposit 20 to 50 eggs in a spherical case. She can produce two to five such batches of eggs during her lifetime. Laboratory-raised individuals can live for two to three years. The young require about one year to mature.

The brown recluse, L. reclusa , in its normal range, prefers to inhabit gaps under rocks, boards, and the bark of dead trees and logs. In structures, it will live inside cracks in walls and boards and behind and under any number of items in storage. The brown recluse prefers nesting sites that are warm and dry. In contrast, L. rufescens prefers to nest in cooler, more humid places.

Medical Importance

The bite of the brown recluse spider is often not immediately painful, although a slight stinging sensation may be felt. This spider’s venom includes a neurotoxic component, but the principal concern is its necrotic or cytotoxic properties, which cause it to destroy the tissue where it is injected. About seven hours after a bite, a small blister-like sore appears that will grow in size. There may be a generalized or systemic body reaction in sensitive individuals. Symptoms include chills, fever, bloody urine, fatigue, jaundice, pain in the joints, nausea, rash, and in extremely rare cases, convulsions and death. The amount of damage depends on the amount of venom injected. The damaged area may be the size of a dime or as large as 20 centimeters in diameter. Affected tissue becomes gangrenous, turns black, and eventually sloughs off, leaving a depression in the skin. Healing is slow and scar tissue results from the wound. Healing may take six to eight weeks or require up to a year if the wound is large.

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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