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Are spider bites dangerous?

Pathologist, WebMD Medical Expert
Medical Editor/Author, MedicineNet

Most spiders do not have mouth parts strong enough to penetrate human skin, and the majority of spiders found in the U.S. are actually harmless. There are two notable exceptions, the black widow spider and the brown recluse spider, which are both dangerous to humans. Spider bites are fortunately uncommon. In many cases, presumed spider bites are actually due to another skin condition or an insect sting.

The black widow and brown recluse spiders are more common in the southern U.S. They prefer warm, dry climates and undisturbed areas such as basements, closets, woodpiles, attics, or under sinks. The black widow spider is a small, black, shiny spider with a red hourglass marking on its belly. The brown recluse spider is sometimes termed a "violin spider." It is about an inch long and has a marking resembling a violin on the upper part of its back.

Bites from both the black widow and brown recluse spiders are dangerous to humans and require prompt emergency medical care.