The first sign that someone may have bed bugs is usually bed bug bites while sleeping. Bed bugs are attracted to warmth and carbon dioxide and bite humans by piercing the skin with two tubes, one to inject anesthetics and prevent clotting and the other to suck blood. Signs of an infestation beyond bites include blood stains from crushed bugs or rust-colored spots from digested blood on bedding and walls, as well as fecal spots, eggshells, or shed skins near hiding places. To be certain a bite is from a bed bug, pictures of typical bed bug bites should be viewed.