Bed bug look-alikes

Order: Hemiptera
Family: Cimicidae


The eastern bat bug (Cimex adjunctus), western bat bug (Cimex pilosellus), swallow bug (Oeciacus vicarius), and Hesperocimex coloradensis are close relatives of bed bugs (Cimex lectularius) and can occur in Colorado homes. The western bat bug is found throughout the state, while the eastern bat bug is only found in parts of eastern Colorado. Both bat bug species feed on the blood of roosting bats, while the swallow bug feeds on the blood of cliff or barn swallows, and H. coloradensis feeds on the blood of purple martins, woodpeckers, and owls. These parasitic insects can occur in homes with roosts or nests of wild animal hosts.
Like bed bugs, these closely related insects are red- or gray-brown, measure about 9.5 mm (3/8 inch) long, and lack wings. Their oval bodies are flattened when unfed and become swollen after a blood meal. Accurate identification is possible upon close inspection with a hand lens or microscope and involves looking at the patterns of hairs and morphology of antennae. In bat bugs, the fringe hairs just behind the head are longer than the width of the eyes, while in bed bugs, these hairs are shorter than the width of the eyes. In swallow bugs, the last two antennal segments are nearly equal in length, while in bed bugs the last two segments are not equal in length and the last segment of the antennae is nearly half the length of the segment preceding it.

Quick Facts

  • Bat bugs and certain bird-feeding bugs are closely related to bed bugs and are similar in size and color. However, several key morphological differences are evident upon close inspection with a hand lens.
  • While bed bugs are associated with beds or sofas, bat bugs and bird-feeding bugs are found near roosting or nesting sites for bats or birds, respectively. When wild animals roost or nest indoors, bat bugs or bird-feeding bugs can seek out alternative hosts for a blood meal.
  • Although bat bugs and bird-feeding bugs can bite humans, they cannot reproduce on human blood.
  • Excluding wild animal hosts, such as bats and cliff swallows, will help prevent or eliminate household infestations of these parasitic insects.
bed bug infestation

Adult western bat bug. Note that the fringe hairs just behind the head are longer than the width of the eyes, a feature that is only visible with magnification. Image credit: Whitney Cranshaw, Colorado State University,

bed bug bites

Adult swallow bug. Note that the last two antennal segments are nearly equal in length (arrows). Image credit: Kansas Department of Agriculture,

bed bug eggs

Adult bed bug. Note that the fringe hairs just behind the head are shorter than the width of the eyes, and the last two antennal segments are not equal in length (arrows). Image credit: James D. Young, USDA APHIS PPQ,

Life history and habits

All these insects develop and reproduce on different hosts. Only bed bugs can reproduce on human blood and are found near beds or other areas where humans sleep. Bat bugs, swallow bugs, and H. coloradensis can only reproduce on the blood of their wild animal host and tend to occur around roosting areas or nests. These species have similar life history, with eggs laid in cracks or crevices near resting areas of the host animal. Upon hatching, nymphs immediately seek out a host animal and begin feeding on blood until fully engorged, which takes only a few minutes. The nymph then moves to a nearby hiding place to digest the blood meal, and gradually molts through several instars until reaching adulthood. After mating, females begin laying eggs over months and continue feeding on blood meals periodically. The exact behavior depends on the pest species.

Bat bugs: Both eastern and western bat bugs are only found in buildings that harbor roosting bats. They tend to be found in the upper areas of buildings where bats are likely to roost such as attics, between walls, in chimneys, and under shingles. Bat bugs often move off the bat after feeding but can also hide in the folded wings of a resting bat and be transported to new roosting areas when the bat migrates. Bat bugs can live seven or eight months without feeding, and when bats are excluded from the building or die, bat bugs will migrate into living areas where they are more likely to encounter humans. Bat bugs are most likely to be found on the building’s upper floor near the roosting site, unlike bed bugs who tend to reside near human resting areas such as beds, chairs, and sofas. Furthermore, bat bugs are typically spotted individually rather than in aggregations like bed bugs.

Swallow bugs: Swallow bugs feed on the blood of swallows, with cliff swallows (Petrochelidon pyrrhonata) serving as the main host. Cliff swallows build jug-shaped mud nests on cliffs or overhangs of man-made structures. A single nest can be used for multiple years, and when a nest is abandoned for the winter, swallow bugs move to nearby sheltered areas such as cracks and crevices where they can survive without feeding for months. Swallow bugs are more likely to bite humans in spring before swallows return to the nests or in autumn after swallows have abandoned the nest. In the spring, swallow bugs are highly starved and may aggressively seek out alternate hosts for a blood meal.

Hesperocimex coloradensis: This species is rarely reported in Colorado homes, and there are no conclusive reports that this species bites humans. This insect can be found in homes where a woodpecker or flicker has constructed a nest, and the nest is occupied by a suitable bird host. After the nest is abandoned, H. coloradensis may wander into living areas of the home.



Excluding animal hosts from returning to roosting or nesting sites within buildings will cause infestations of bat bugs, swallow bugs, or H. coloradensis to die out. When host animals are absent in October through early April, entry points into the building can be sealed with screening or other barriers. When bats hibernate in the building, installing a one-way door can help evict bats in early spring before they produce young. It is worth noting that bats are protected under Federal law and their removal involves important health considerations such as the transmission of rabies. For these reasons, seeking out professional help is highly recommended.
After the animal host has been excluded from the building, the remaining bat bugs or bird-feeding bugs can continue wandering through the structure for several months in search of a blood meal. Their movement can be restricted by sealing cracks around windows, gaps around electrical sockets, or other holes and cracks in walls. They will starve to death eventually, but in certain conditions can survive over a year without a blood meal. Applying insecticide dusts or sprays into cracks and crevices can speed up the elimination of bat bugs and bird-feeding bugs. To be effective, insecticides must have residual activity, and it is recommended to seek professional assistance when applying insecticides for these pests.

CSU Extension Fact Sheet

Download or view the CSU Extension’s PDF fact sheet for your reference.


Cranshaw, W., M. Camper, and F. Peairs. 2013. Bat Bugs, Bed Bugs and Relatives. Colorado State University – Extension. Available