Cluster flies are flies of the genus Pollenia in the family Polleniidae. Unlike the more familiar blow flies, such as the bluebottle genus Phormia, they are completely harmless to human health because they do not lay eggs in human food.

What causes cluster flies?

What Causes Cluster Flies? Cluster flies enter your home for a very simple reason: They are seeking warmth in order to survive the cold winter months. These are mostly outdoor insects that lay eggs in the soil, which hatch into larvae that feed on earthworms.

What are cluster flies attracted to?

Cluster flies are attracted to light, which explains their fixation with windows on sunny days. They are also attracted to artificial lights at night. These flies are not attracted to garbage and other refuse like so many other types of filth flies.