Pollenia rudis

Pollenia rudis, the common cluster fly, is a species of fly in the family Polleniidae. Pollenia rudis is also known as the attic fly, the loft fly, pollenie du lombric [French], and the buckwheat fly. During the autumn and winter months, Pollenia rudis can be found overwintering inside attics or lofts. This sluggish species can be found “clustering” near the interior windows of a warm structure.

This species is widely distributed throughout the United States, Canada, and Europe and is considered a pest species in structures. P. rudis can be found wherever their host earthworm, the Allolobophora genera (also known by the genus name: Aporrectodea), occurs. These earthworms are typically located in well-drained, silt-loam soil with grass cover. During the summer, P. rudis can be found in fields and open areas. It is only when there is a sudden drop in temperature that the cluster fly shifts to the interior of structures, holes in trees, loose bark, or other crevices and cavities.