Cluster flies, also known as attic flies, are household pests.
Length: Adults measure 8 to 10 millimeters.
Body: Light and dark gray-checkered abdomens. The thorax of an adult cluster fly is covered in short, golden hairs and the wings overlap when at rest.
Characteristics: Cluster flies are slightly larger and darker than the common housefly and move more sluggishly.
The cluster fly life cycle begins when a female lays her eggs in the soil in late summer or early fall. These eggs hatch within a few days, after which larvae seek to enter the body cavities of earthworms. Cluster flies' development time from egg to adult is about 27 to 39 days.
Cluster fly larvae feed on earthworm hosts for several days, at which time they molt and pupate in the soil.