Cluster Flies
Common Name
Scientific Name
Cluster Flies
Pollenia rudis
Identification:
Adult cluster flies are slightly larger than the common house fly. They are dull-gray with black markings and have golden-yellow hairs on the thorax, which can give the appearance of a golden sheen. These medium-sized insects are 1/4 inch to 3/8 inch in length. The hairs are more numerous on the under side of the thorax between and near the legs. Another noticeable feature of the Cluster Fly is the way its wings are held flat over its back while resting; the wing tips overlap when held in this position. The immature stages, egg and larva, are seldom seen as the eggs are deposited on the soil and the larva or maggots burrow into earthworms on which they feed. The maggots are cream colored and are an elongated wedge shape.
Biology:
Cluster fly females lay their eggs singly in cracks in the soil; the larvae emerge in three days and begin to seek out their food source: earthworms. After burrowing into the earthworm, basically becoming a parasite in the earthworm, the larvae feed for about three weeks before pupating. The adult Cluster Fly emerges from its pupa after 12 to 14 days. The adult flies (of which there 3 to 4 generations per year) feed on flowers.
Habits:
Adult cluster flies will begin to hibernate when the days get shorter in mid-August and move to a protected area for the winter. When Cluster Flies come out of hibernation, they will cluster together on warm sides of buildings during the day. When the sun goes down and the temperature begins to cool, they will crawl into buildings through cracks, under eaves, gaps in siding, cracks in windows, etc. They will group together in attics, empty or unused rooms, wall voids, basements, tree holes, and other darkened areas. They are attracted to light, light colored siding, and other structures on lawns, especially areas that are inhabited by earthworms.
