A poisonous spider (Loxosceles reclusa) native to parts of the American Midwest, though they have been reported on both the East and West Coasts. About a quarter- to three-quarters of an inch long, this tan or brown colored spider is sometimes called the fiddleback, due to the small, dark, violin-shaped mark on its head and back. They are not hairy spiders, so they can be easily distinguished from the wolf spiders, which have a similar appearance.

Egg cases are off-white in color and silken. They are about a third of an inch in diameter and are found in sheltered, dark areas. They hatch in about 24-36 days, but the baby spiders develop slowly -- they reach maturity in about ten to twelve months and can survive for a long time without food or water.

The brown recluse's poison has a necrotizing effect -- it causes skin around the bite to begin to rot away and slough off. After someone is bitten, they will often show a reaction in about 24-36 hours. They will often be restless and will feel fever, chills, nausea, joint pain, and weakness. In some severe cases, the bite wound may last for months, and a scar will often develop. Some people, however, are not harmed by the bite at all. In any case, the poison is rarely fatal -- small children and the elderly would be in the most danger if bitten.

The brown recluse likes to hang out in dark, unused areas, so be careful rummaging in that attic or toolshed -- or that old shoebox. Luckily, they're rarely aggressive, but if you threaten them -- say, by sticking your hand into dark places in your garage -- they may attack. If you're bitten by a brown recluse, see a doctor right away. Kill the spider, if possible, and take it to the doctor with you. If you have shoes on, they're easy to squish, or you can spray 'em with bug spray.

Research from http://www.ext.vt.edu/departments/entomology/factsheets/brownrec.html