Brown Recluse Spider " Loxosceles reclusa "

The brown recluse, Loxosceles reclusa, Sicariidae (formerly placed in a family "Loxoscelidae") is a recluse spider with a necrotic venom. Similar to other recluse spider bites, their bite sometimes requires medical attention.

Brown recluse spiders are usually between 6 and 20 millimetres (0.24 and 0.79 in), but may grow larger. While typically light to medium brown, they range in color from whitish to dark brown or blackish gray. The cephalothorax and abdomen are not necessarily the same color. 

These spiders usually have markings on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nicknames fiddleback spider, brown fiddler, or violin spider.

The brown recluse bears a potentially deadly hemotoxic venom. Most bites are minor with no necrosis. However, a small number of brown recluse bites do produce severe dermonecrotic lesions (i.e. necrosis); an even smaller number produce severe cutaneous (skin) or viscerocutaneous (systemic) symptoms. 

In one study of clinically diagnosed brown recluse bites, skin necrosis occurred 37% of the time, while systemic illness occurred 14% of the time.In these cases, the bites produced a range of symptoms common to many members of the genus Loxosceles known as loxoscelism, which may be cutaneous and viscerocutaneous. 

In very rare cases, bites can even cause hemolysis the bursting of red blood cells.