brown recluse spider or violin spider, poisonous nocturnal spider, Loxoceles reclusa, most common in the SE and S central United States. Adults are 3/8 in. (10 mm) long and are light brown with a dark, violin-shaped mark on the back near the head. In humans their venom kills the tissue surrounding a bite and leaves a deep sore, but only rarely does a bite result in death.

Venomous species (Loxosceles reclusa) of brown spider, most common in the western and southern U.S. The brown recluse is light-coloured, generally with a dark violin-shaped design on its back, for which it is sometimes called the violin spider. About 0.25 in. (7 mm) long, it has a leg span of about 1 in. (2.5 cm). It has extended its range into parts of the northern U.S. and is often found under stones or in dark corners inside buildings. The venom of the brown recluse destroys the walls of blood vessels near the site of the bite, sometimes causing a slow-healing skin ulcer. Bites are occasionally fatal.

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