Bites of brown recluse spiders and suspected necrotic arachnidism.

N Engl J Med 2005;352:700-7. Copyright © 2005 Massachusetts Medical Society. utaneous injury caused by spider venom has been recognized by physicians in the United States only since the late 1950s, with recluse spiders (genus loxosceles) most frequently implicated. During the past five decades, the growing popular belief that spiders cause many cases of skin necrosis in the United States has resulted in the presumption that brown recluse spiders are to blame, even in geographic areas where they are extremely rare or nonexistent. Among both physicians and the general public, the perceived threat of spider bites far exceeds the actual risk. The misdiagnosis of spider bites is given to a wide spectrum of dermatologic conditions, some of which are far more dangerous than a spider bite. Although much has been published about the pathophysiology and treatment of necrotic spider bites, therapeutic interventions continue without evidence-based justification. Nearly 40,000 species of spiders have been described worldwide. 1 Almost all spider venom probably evolved for paralyzing prey — mostly insects, other arthropods, or small vertebrates. Although some spiders have defensive venom, it is usually not directed at humans and has little or no effect on mammalian tissue. A few spiders can cause deleterious envenomation, but most produce only minor injury; some are capable of causing skin necrosis in humans. Although humans have always coexisted with spiders, the notion that spiders may cause necrotic skin ulcers is modern. Less than a century ago, Schmaus 2 first established the connection between spider bites and human skin injury (ulceration) in a case report documenting the bite of Loxosceles reclusa (reported as L. rufescens ). In 1947, Macchiavello 3