Cluster fly


The grass flies or cluster flies or attic flies are the genus Pollenia in the family Polleniidae are completely harmless to human health. They are strictly parasitic on earthworms; the females lay their eggs near earthworm burrows, and the larvae then feed on the worms. Cluster flies seek refuge in cold weather and find their way into attic spaces and similar areas indoors. They often emerge on warm days, and cluster at windows attempting to exit.
The typical grass fly Pollenia rudis is about 7 mm long and can be recognised by distinct lines or stripes behind the head, short golden-coloured hairs on the thorax, and irregular light and dark gray areas on the abdomen. Cluster flies are typically slow-moving.
Cluster flies have a widespread distribution. Eight species are found in Britain and 31 in Europe. Pollenia species are also numerous in Australia and New Zealand ; they are common in North America. P. rudis has spread widely in association with humans.

Species