Recluse spiders, which also include Loxosceles rufescens, build irregular webs that frequently include a shelter consisting of disorderly threads. Unlike most web weavers, they leave these webs at night to hunt. People get bitten when they unintentionally squeeze them in clothing and bedding.
These spiders frequently build their webs in woodpiles and sheds, closets, garages, and other places that are dry and generally undisturbed.
As indicated by its name, this spider is not aggressive and usually bites only when disturbed. Actual brown recluse bites are rare. The initial bite frequently cannot be felt. Most bites are minor with no necrosis, but a small number produce severe systemic conditions. The serious bites form a necrotising ulser that destroys soft tissue and may take months to heal, leaving deep scars. Initially there may be no pain, but over time the wound may grow to as large as 10 inches (25 cm). Death occasionally results.
First aid involves the application of an ice pack to slow spread of the poison, and prompt medical care. Take the spider with you if you can find it.
Other conditions are often misdiagnosed as brown recluse bites. It is estimated that 80% of reported brown recluse bites could be misdiagnoses. The misdiagnosis of a wound as a brown recluse bite could delay proper treatment of serious diseases (Article.).
There is now a test for brown recluse venom that can determine if a wound is a brown recluse bite.