Bed bugs are parasitic insects in the genus Cimex that feed exclusively on blood. Cimex lectularius, the common bed bug, is the best known as it prefers to feed on human blood; other Cimex species specialize in other animals, e.g., bat bugs, such as Cimex pipistrelli (Europe), Cimex pilosellus (Western United States), and Cimex adjunctus.
The name bed bug derives from the preferred habitat of Cimex lectularius: warm houses and especially near or inside beds or other sleep areas. Bed bugs are mainly active at night, but are not exclusively nocturnal. They usually feed on their hosts without being noticed.
A number of adverse health effects may results from bed bug bites, including skin rashes, psychological effects, and allergic symptoms. Bed bugs are not known to transmit any pathogens as disease vectors. Certain signs and symptoms suggest the presence of bed bugs; finding the adult insects confirms the diagnosis.