Cobweb spiders, part of the family Theridiidae, are commonly found in and around your home. The majority of them are harmless. There are over 2,300 species of cobweb spiders, and more than 230 in the US. They are named for their messy, irregular webs, which can help you identify them. You can also identify this type of spider by their round bellies, their long legs, and their tendency to live in dark corners.