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 tubes to inject saliva and suck blood. Bed bug bites can resemble mosquito or flea bites but often appear in a linear pattern from being disturbed while feeding. Other signs of bed bugs include blood stains, rust-colored spots from excrement on bedding, and seeing fecal spots, eggshells or shed skins near hiding places.