Cluster Flies

Key Features of Cluster Flies

These are dark greyish flies about 8mm long with yellowish hairs on the back and with overlapping wings.

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, the larvae feed for about three weeks before pupating. The adult Cluster Fly emerges from its pupa after 12 to 14 days. There are 3 to 4 generations of adult flies per year and these feed on flowers.

In autumn they congregate in large numbers in upper rooms or roof spaces of houses to hibernate. The larvae of one species are parasitic upon certain earthworms, so this species is more common in rural areas.

A mass of cluster flies has a characteristic smell. They are sluggish in flight and are a nuisance in the house.