The brown recluse spider (Loxosceles reclusa) is the prototypical member of the genus Loxosceles, which as a group can produce necrotic arachnidism following envenomation. These small spiders (approximately 1 cm in body length and 3 cm in leg length) have a worldwide distribution and are identified by fiddle-shaped markings on their anterodorsal cephalothorax. Initial envenomation may be painful, although patients often report no recollection of being bitten. Initial stinging gives way to aching and pruritus. The wound then may become edematous, with an erythematous halo surrounding a violaceous center. The erythematous margin often spreads in a pattern influenced by gravity, leaving the necrotic center near the superior aspect of the lesion. Bullae may erupt, and—over a period of 2 to 5 weeks—the eschar sloughs, leaving a deep, poorly healing ulcer. In approximately 10% of cases, systemic symptoms (loxoscelism) are present. Systemic features of brown recluse envenomation may include fever, nausea, vomiting, headache, morbilliform rash, arthralgias, and, in severe cases, hemolytic anemia, coagulopathy, renal failure, and even death. Children are at higher risk of systemic disease.
Brown Recluse Spider. Brown recluse spider with characteristic “fiddle” marking on the anterodorsal aspect of the cephalothorax. (Photo contributor: R. Jason Thurman, MD.)
Fiddle Back Marking. A close-up look at the characteristic fiddle back marking of the brown recluse spider. (Photo contributor: R. Jason Thurman, MD.)
Early Brown Recluse Spider Bite. Early brown recluse spider bite (approximately 8 hours) with a violaceous center surrounded by faint-spreading erythema. Note the “red, white, and blue” appearance. (Photo contributor: Lawrence B. Stack, MD.)
Later Recluse Spider Bite (24 hours). Brown recluse spider bite at approximately 24 hours. Note asymmetric spread of erythema and early central ulcer formation. (Photo contributor: Edward Eitzen, MD, MPH.)
Recluse Necrosis (Weeks). Within about 2 to 5 weeks, significant brown recluse envenomations may produce a deep, poorly healing ulcer with necrosis. (Photo contributor: Kevin J. Knoop, MD, MS.)
Management and Disposition
Most cutaneous lesions secondary to brown recluse spider bites can be managed with cold compresses, elevation, loose immobilization, and tetanus prophylaxis. Severe lesions may require reconstructive plastic surgery several weeks after wound stabilization. Dapsone, recommended in the past, should not be used. Any systemic reaction with evidence of hemolysis, hemoglobinuria, or coagulopathy should prompt admission. Hyperbaric oxygen therapy and antivenom (not available in the United States) have been suggested as possible adjuncts, but no clear consensus of preferred treatment has been established.