Cluster fly is a collective name given to several species that spend winter as adults in sheltered places, including inside homes and structures.
They tend to accumulate in wall voids, attics, and rooms with southern or western exposures. One or more species in this group may be present.
While cluster flies are an annoyance, they do not breed indoors, and they do not cause any damage. The flies will become active on warm days, crawling and flying to windows in an attempt to escape outside.
Cluster fly species