These spiders are chocolate brown in color, and their bodies are about 11/32 inch in length with long legs. They have 3 pairs of eyes, arranged in a triad, and a violin-shaped marking on the cephalothorax. The body of the "violin" is near the eyes and the neck of the "violin" extends backward, ending before the abdomen. Males are similar to females in appearance.

The brown recluse, in its normal range, prefers to inhabit gaps under rocks, boards, and the bark of dead trees and logs. In structures, it will live inside cracks in walls and boards and behind and under any number of items in storage. The brown recluse prefers nesting sites that are warm and dry.

Medical Importance: The bite of the brown recluse spider is often not immediately painful, although a slight stinging sensation may be felt. This spider's venom includes a neurotoxic component, but the principal concern is its necrotic or cytotoxic properties, which cause it to destroy the tissue where it is injected. About 7 hours after a bite, a small blister like sore appears that will grow in size. There may be a generalized or systemic body reaction in sensitive individuals. Symptoms include chills, fever, bloody urine, fatigue, jaundice, pain in the joints, nausea, rash, and in extremely rare cases, convulsions and death. The amount of damage depends on the amount of venom injected. The damaged area may be the size of a dime or as large as 25/32 in diameter. Affected tissue becomes gangrenous, turns black, and eventually sloughs off, leaving a depression in the skin. Healing is slow and scar tissue results from the wound. Healing may take 6 to 8 weeks or require up to a year if the wound is large.