Loxoscelism, or envenomation by the brown recluse spider, may result in necrotic lesions and systemic reactions, including hemolytic anemia. Histologically, it resembles a cutaneous Arthus reaction. The reaction mechanism involves interactions between complement, neutrophils, and the clotting system. It is best treated with analgesics, avoidance of early surgical debridement, and oral dapsone.