Cluster Fly Invasion
Get ready for a fly invasion!
Do you have flies hibernating in your home in late summer/fall? Your new house pests may be attic flies or cluster flies. Adult cluster flies gather in clusters in warm buildings to overwinter. They are considered a household nuisance. The name is derived from tight “clusters” made by hibernating individuals in wall voids or attics, throughout Canada, most of the United States and Europe. On the first warm days of spring you may notice cluster flies gather outdoors, buzzing on lawns. They may also congregate in huge numbers on sunny walls in the fall.
The adult cluster fly looks like a very large house fly. The difference is that at rest, the fly overlaps its wing tips over the abdomen, like a pair of scissors, while the house fly does not. The cluster fly is dark gray to almost black with a checkered grayish abdomen. There are numerous short crinkly golden hairs on the sides of the thorax. In old specimens, these can be rubbed off. The fly is a sluggish flyer, buzzing loudly while flying aimlessly in concentric circles in buildings. Although this pest is less hazardous than other infestations, you don’t want cluster flies in your home or building.