Spider bites are usually harmless. Many bites attributed to spiders turn out to have been inflicted by other bugs. Skin infections also have been mistaken for spider bites.
Only a few types of spiders have fangs long enough to penetrate human skin and venom strong enough to severely affect a human being. In the United States, these include the black widow spider and the brown recluse spider.
Black widow spider bites can cause severe abdominal pain or cramping. Brown recluse spider bites can cause a sting or sharp pain, like a bee sting. With severe bites, surrounding skin may die within a few hours. Both types of spiders generally live in undisturbed areas, such as attics or sheds. And they don't bite unless threatened.