Cluster Flies vs. House Flies in New Construction Home

In a newly built home, about 20 flies were found clustered in one corner of the dining room ceiling. The homeowner wonders why they stay in such a confined area.

Identification: Cluster Flies

These are almost certainly cluster flies (Pollenia spp.), not house flies. Cluster flies resemble house flies but behave differently: they enter homes in large numbers in fall, cluster together in attics, wall voids, and upper rooms, and become active on warm winter days.

Biology and Habitat

Cluster flies are parasites of earthworms. They thrive near well-managed turf—golf courses, cemeteries, athletic fields, and horse pastures—that support healthy earthworm populations. New construction near such areas is especially prone to infestations.

Management

Cluster flies are harmless but annoying. Control focuses on exclusion (sealing entry points) and vacuuming or trapping indoor flies. For detailed life history and control methods, see livingwithbugs.com/cluster.html.