Latin Name:  Pollenia sp.
                        (P. Beuk, det.)

Length:  6 to 8 mm

Range: Throughout Alberta

Habitat:  Various

Time of year seen:  Spring to fall.

Larval Diet:  Earthworms

Other:  Cluster flies can be found in and on most buildings and other structures.  In the spring and fall flies cluster on the warm, sunny sides of buildings with light colored siding or that are near grassy areas with earthworms.  As the weather becomes cooler, they move into protected places (i.e. buildings) to hibernate.  Reproductive activity occurs outside after the flies leave their refuges in the spring.  The female fly lays her eggs in soil that has earthworms.  The eggs hatch in three days and the larvae burrow into an earthworm and begin to consume it. This stage takes from 13 to 22 days at which point the larva pupates for 11 to 14 days before emerging as an adult fly. There are usually four generations per year.  Adult flies are non-metallic grey with lighter and darker grey patches on the abdomen, the thorax has crinkly hairs and is not distinctly striped and the wing tips are overlapped when the fly is at rest. (http://ohioline.osu.edu/hyg-fact/2000/2110.html)