The brown recluse or the fiddle-back or the violin spider belongs to the genus Loxosceles reclusa. It is brown and carries a violin shaped marking on the upper portion of its body where the legs are connected with the neck of the “fiddle” extending to the tail. All recluses do not have this marking. For example, young brown recluse's often do not carry this mark. It can also be distinguished by its six eyes rather than three and a lack of any other patterning on its body. There are no marking on the abdomen or legs, only on the cephalothorax. It measures about 8–15 mm in body size, with longish legs around 2–3 cm long.
The brown recluse is usually a reclusive non-aggressive spider found living in dark and uninhabited spaces away from humans and animals. They are active at night. Bites usually occur when the spider becomes trapped and an animal or human rolls over on the spider or when an animal disturbs the spider in its space.
Reaction from the bite typically causes an ulcerated necrotic wound resulting in the death of the surrounding soft tissue. The wound is slow to heal. Serious complications occur when the ulcer becomes a gangrene or when the venom enters the blood stream and is carried to the internal organs. Destruction of red cells, renal failure, coagulation disruption, and death are all possible known complications of a recluse bite. These complications are rare but have been known to occur.
The bite may present with no particular symptoms or just a simple localized pain and stinging that may last 6–8 hours followed by itching and soreness. A white lesion may be seen with a dark central scab on an uneven red background. After 2–5 weeks the central scab may slough leaving a deep, slow healing ulcer that usually kills soft tissue while sparing muscle tissue. In case the venom spreads to the blood stream it may present with symptoms like anemia with bloody urine in the first 24 hours. Other possible systemic manifestations within the first 2–3 days after the bite – fever, chills, rash, weakness, rapid growth of white blood cells, nausea, joint pain