blog post
Cluster fly

Cluster fly

Cluster flies are the genus Pollenia in the blowfly family Calliphoridae. Unlike more familiar blowflies such as the bluebottle genus Phormia, they do not present a health hazard because they do not lay eggs in human food. They are strictly parasitic on earthworms; the females lay their eggs near earthworm burrows, and the larvae then infest the worms. However, the flies are a nuisance because when the adults emerge in the late summer or autumn they enter houses to hibernate, often in large numbers; they are difficult to eradicate because they favor inaccessible spaces such as roof and wall cavities.

They are often seen on windows of little-used rooms. They are also sometimes known as attic flies.

The typical cluster fly Pollenia rudis is about 7 mm long and can be recognized by distinct lines or stripes behind the head, short golden-colored hairs on the thorax, and irregular light and dark gray areas on the abdomen. Cluster flies are typically slow moving.