Black Widow spiders build webs near entrances of abandoned burrows, outbuildings, or under stones. They seldom leave their webs. These spiders eat small insects or small creatures caught in their web such as mice or lizards. Black Widows are well know for their toxic venom, the venom subdues their prey. They are not inclined to bite humans,  although the venom can be harmful. Only bites from the females are dangerous to humans, while the males and juveniles are harmless. The females are black or dark brown with a red or dark orange hourglass marking on their abdomen. The males have red markings on the upper part of the abdomen that looks like bars or spots, the juveniles are similar to the males. Here is a female Black Widow.