While the main insect of concern in the genus Cimex is the common bed bug, which prefers human blood, there are other insects related to bed bugs which are similar in appearance and habit. It is important to obtain a positive identification if there is any question as to the identity of the pest.
The tropical bed bug is closely related to the common bed bug in that it prefers to feed on humans; however, the tropical bed bug is not as widespread as the common bed bug.
Bugs Mistaken for Bed Bugs
There are several species of insects which resemble the bed bug but have other preferred food sources. When the normal food source is unavailable, though, these insects might feed on humans. Some of these pests might not feed on humans but might bite until the insect realizes that the food source is not preferred.
Within the family Cimicidae, which the genus Cimex is a member, there are species which are not normally found in human dwellings but might be accidentally introduced via hosts, migration from former feeding areas, or by transporting by humans.
European Swallow Bug
The European swallow bug feeds on a broader list of birds than just swallows and will enter buildings and feed on humans if their normal bird hosts are unavailable. Its preferred hosts, swallows, may have nests which become infested by swallow bugs.
Swallows might abandon nests, but the swallow bugs can emerge in warm weather in anticipation of the return of the swallows. If these birds do not return, the swallow bugs will move and can find their way into the living space of a home, where they feed on humans.
Eastern Bat Bug
The eastern bat bug is a common insect in attics or where bats are present and may easily work their way into a structure and feed on humans. The eastern bat bug, found mostly in the eastern part of the United States, is probably the most common insect easily mistaken for a bed bug. There are several characteristics which distinguish the bat bug from the bed bug and these can be easily observed using a hand lens or microscope. There is a western bat bug, but there are no documented cases of this insect attacking humans, even if they infest homes.
Prior to the recent common bed bug resurgence, the bat bug was probably the most common insect related to a bed bug that humans encountered. The bat bug experience has since been overshadowed by the common bed bug. The chimney swift bug lives in nests of the namesake birds and will bite humans if they have no other source of food; however, they usually do not cause massive infestations.
The Poultry Bug
The poultry bug (Haemotosiphon inodorus) is found near birds and is a common pest of chicken and duck houses. These bugs hide near where the birds roost and will emerge at night to feed. If humans remain in close proximity with poultry, these bugs can feed on humans, although their preferred food source is poultry and fowl.
Picture of bugs that resemble bed bugs: