The genus Cimex includes the common bed bug, Cimex lectularis, and the tropical bed bug, C. hemipterus, as well as related bugs that normally feed on bats and birds. Cimex lectularis is the most common species to feed on humans and has experienced a resurgence worldwide. Adult bed bugs are red to brown, measure up to 5 mm long by 3 mm wide, and have a flattened, oval-shaped body. They have segmented abdomens which gives them a banded appearance. They have no hind wings and only rudimentary (vestigial) front wings that have been reduced to pad-like structures. Bed bugs can be differentiated from similar-appearing bat bugs by the length of the hair-like structures on their heads: the hairs are shorter than the width of the eye in bed bugs and longer than the width of the eye in bat bugs. Differentiating the two bugs may be important for pest control efforts. Immature bed bugs (nymphs) have a similar appearance as the adults but are smaller.