The swallow bug (Oeciacus vicarius) is a parasitic insect that feeds exclusively on blood. This ectoparasite primarily targets swallows. When their preferred hosts abandon their nests, the bugs can quickly become a nuisance to humans. Their presence in a home indicates an active or recently abandoned bird nest on or near the structure.
Identification and Comparison to Bed Bugs
Swallow bugs are small, wingless insects belonging to the family Cimicidae, the same family as the common bed bug (Cimex lectularius). Adults are flat, oval-shaped, and about 0.2 to 0.3 inches long. They are grayish-brown, darkening to reddish-brown after a blood meal. Their close physical resemblance often requires professional inspection for accurate identification.
Microscopic examination reveals key differences between the species. Swallow bugs have longer, finer hairs across their body compared to the common bed bug. A precise identifying characteristic is found in their antennae. The third and fourth segments of the swallow bug’s antennae are nearly equal in length, while the fourth segment is noticeably shorter in the common bed bug.
Life Cycle and Dependence on Avian Hosts
The swallow bug is an obligate parasite, meaning its entire life cycle depends on an avian host, such as the cliff swallow (Petrochelidon pyrrhonota) or barn swallow (Hirundo rustica). The life cycle includes an egg stage, five nymphal stages requiring a blood meal to molt, and the final adult stage. All stages reside within the mud nests constructed by the bird hosts.
Reproduction is synchronized with the bird’s presence, occurring during the 8 to 10-week nesting season in the spring and summer. When the birds migrate in the late summer or fall, the bugs enter a dormant state. They survive in the unoccupied nests for extended periods without feeding. Studies show they can remain viable for up to a year, waiting for the swallows to return.
Why Swallow Bugs Enter Human Homes
The migration of the avian host triggers swallow bugs to enter human dwellings. When swallows depart for the season, the bugs lose their blood source and become starved. This lack of nourishment drives the insects to abandon the nests, which are often built under eaves, porches, or in attics.
The dispersing bugs crawl from the empty nests into the nearest structure, searching for a new blood meal. They are small enough to enter through tiny cracks, utility openings, or window screens. Once inside, they will bite humans, causing reactions from minor irritation to welts. While they are not known to transmit human diseases, they cannot establish a permanent, breeding infestation in a home because their reproductive cycle requires avian blood.
Prevention and Professional Removal
Prevention must focus on managing swallow nests, though this is complicated by federal law. Swallows are protected under the Migratory Bird Treaty Act, which prohibits the removal of any active nest containing eggs or chicks. The most effective prevention is to discourage nest building before the swallows return in the spring by installing exclusion devices, such as netting or specialized panels.
Nest removal and treatment should occur after the birds have fully migrated, typically in the late fall or winter. Simply tearing down the nest is not sufficient, as the bugs will have already dispersed into the structure. Professional pest control is necessary for effective eradication. Treatment focuses on the exterior areas where the nests were located, as well as cracks and crevices near entry points.
Exterminators apply residual insecticides, often containing pyrethroids like deltamethrin or bifenthrin, to exterior wall voids, eaves, and window frames to intercept the migrating insects. This specialized treatment targets bugs that have moved into the structure, preventing them from seeking humans as an alternative host. Treating the source and creating a protective chemical barrier is the best strategy to eliminate the population and prevent re-entry.