Although all spiders use venom when they bite and kill their prey, the black widow and the brown recluse spiders are the only North American species consistently dangerous to humans. Under most conditions outdoors, spiders are considered beneficial because they feed on insects. However, they are undesirable to most homeowners when indoors, and the unsightly webbing spiders use to catch insect prey usually outweigh this beneficial behavior. Many spiders are associated with moisture and, therefore, are found in basements, crawl spaces, and other damp parts of buildings. Others live in warm, dry places so are found in subfloor air-vents, in upper corners of rooms or in attics.
Most species hide in cracks, darkened areas, or other retreats which they construct of silk.
The black widow is widely distributed over the warmer portions of the United States. Females are easily identified because of their globular, shiny black abdomen with two reddish or yellowish triangles on the underside. These reddish or yellowish triangles form a characteristic hourglass marking. Males are much smaller and lighter-colored, with light streaks on their abdomens. The black widow's web is an irregular mass of fibers with a small central area to which the spider retreats while waiting until its prey becomes ensnared.