Background: Loxosceles rufescens is a spider that may bite humans. Objectives: To describe the clinical manifestations and treatment of patients with bites caused by L. rufescens, and present scanning electron microscopy of the spider. Materials & Methods: Twelve patients are described, seven with a confirmed aetiological diagnosis as a sample of the spider was captured. In one case, scanning electron microscopy of the spider was performed. Results: Seven patients presented with a single necrotic ulcer of varying morphology, with a purulent-necrotic bed, located on the neck (one patient), buttock (one patient), thigh (one patient), legs (three patients) and foot (one patient). All patients complained of burning and pain. No systemic symptoms were observed. All patients were treated with sodium hypochlorite solution packs, an equine catalase gel, and polyhexamethylene biguanide cream. Oral analgesics were added. In one patient, oral prednisone was prescribed. Two patients with bacterial superinfections were treated with i.v. piperacillin/tazobactam or i.m. ceftriaxone. All patients recovered within eight weeks, however, a scar developed in five of six patients. Conclusion: The sequence of cutaneous manifestations due to L. rufescens bites is typical. At first, erythema and oedema forms, followed by a vesicle, blister or pustule and, finally, an eschar and scar. Systemic symptoms and signs are rare. To consider this spider as an aetiological agent of necrotic ulcers, it is necessary to capture a sample of the spider, dead or alive, which should then be identified by an expert. Corticosteroids, antibiotics and analgesics are frequently used. Surgery is often necessary.
