Black widow spiders are active at night (nocturnal), and they prefer dark areas. They tend to avoid houses where people live, but they may be found in garages or sheds. Only female black widow spiders bite humans, and they only do so if disturbed.
Brown recluse spiders are not aggressive and will only bite if they feel threatened. They prefer dark, warm, dry environments such as attics, closets, basements, barns, and wood piles. Most brown recluse bites occur during the summer. The spider searches for prey at night and rests in the day in its small web, which is usually constructed in corners or crevices.
A black widow spider bite may appear as double fang marks at the site of the bite. The bite is described as feeling like a pinprick, though there may only be a small localized reaction. Blood pressure or heart rate may rise. The severity of the reaction to the bite depends on the age and overall health of the victim. Children and the elderly are usually more seriously affected.