Size: Black widow spiders may have a body up to 3/4-inch in length with the abdomen reaching 3/8-inch in diameter.

Color: The color is typically glossy black but may also be dark brown to light brown.

Related widow spiders may be brown in color. The characteristic red markings on the underside of the abdomen often connect to form an hourglass shape, but this does not always occur. The black widow spider is widely feared because its bite results in severe pain that may take several days to subside. Such bites are rarely fatal but small children and elderly persons are at risk.