The Brown Recluse:

These little buggers are identified by the violin shape on their back. They are native to the Midwestern and Southeastern states--documented populations of these spiders outside of these areas are extremely rare. These small non-hairy spiders are yellowish-tan to dark brown in color with darker legs. Their legs are about one inch in length.
These spiders are not aggressive and bite only when threatened, usually when pressed up against the victim's skin. They seek out dark, warm, dry environments such as attics, closets, porches, barns, basements, woodpiles, and old tires. Its small, haphazard web, found mostly in corners and crevices, is not used to capture prey. Most bites occur in the summer months.
Brown recluse spider bites often go unnoticed initially because they are usually painless bites. Initially the bite site is mildly red and upon close inspection may reveal fang marks. Most commonly, the bite site will become firm and heal with little scaring over the next few days or weeks. Occasionally, the local reaction will be more severe with erythema and blistering, sometimes leading to a blue discoloration, and ultimately leading to a necrotic lesion and scarring.
For more information, go to: http://www.emedicinehealth.com/spider_b ... cle_em.htm