"The brown recluse, Loxosceles reclusa, Sicariidae (formerly placed in a family "Loxoscelidae") is a recluse spider with a necrotic venom. Similar to other recluse spider bites, their bite sometimes requires medical attention. The brown recluse is one of three spiders (the others being the black widow and Loxosceles laeta, the Chilean recluse) with medically significant venom in North America"-Wikipedia.
"While the majority of brown recluse spider bites do not result in any symptoms, cutaneous symptoms occur more frequently than systemic symptoms. In such instances, the bite forms a necrotizing ulcer as the result of soft tissue destruction and may take months to heal, leaving deep scars. These bites usually become painful and itchy within 2 to 8 hours. Pain and other local effects worsen 12 to 36 hours after the bite, and the necrosis develops over the next few days.[34] Over time, the wound may grow to as large as 25 cm (10 inches). The damaged tissue becomes gangrenous and eventually sloughs away"- The Wikipedia article.