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. These webs are frequently constructed underneath boards, stones, or the seats of outdoor privies. They are also found along foundation slabs, behind shrubs and especially where brick or wood siding extends close to ground level. This spider does not usually enter residences. The bite produces a sharp pain similar to a needle puncture.