Most spiders are relatively harmless, but there are a few species — many with extremely potent venoms — that can and will bite a human if they feel threatened. The brown recluse, native to the South-Midwest United States, is one of these. A recluse's bite will induce vomiting, fever, nausea, rashes and muscle or joint pain, and some bites may result in effects as severe as a necrotizing ulcer that can take months to heal.