• Size: Cluster flies are three-eighths to one-half inch long and look similar to house flies
  • Color: Cluster flies are dark gray in color with golden hairs and overlapping wings.
  • Behavior: Cluster flies are parasites of earthworms. In the late spring/early summer, cluster flies lay their eggs in soil cracks, and the maggots enter their earthworm hosts. The complete life cycle from egg to adult cluster fly is about 27 to 39 days. Starting in mid-August, adult cluster flies seek out protected locations—preferably sunny, light-colored buildings. Cluster flies enter a home one at a time, but collect throughout the house in swarms, much like a swarm of bees. They enter homes through small openings such as cracks around your windows or walls and tend to hibernate until warmed by the home’s environment.


Cluster flies like to hibernate in several places in the home, including nooks, under curtains and dark corners. They’re also known as attic flies since they’re usually found in walls in the upper areas of the house such as the attic. On warm sunny days you can find cluster flies on your windowsill attempting to escape, but they’ll go into hibernation when temperatures drop below 54 degrees Fahrenheit.


Tips for Control

Close all points of entrance to prevent cluster flies from entering your home. Fill in cracks around your air conditioning, vents, siding, windows, etc. Pay special attention to the sunny side of your home, making sure screens are in place. If you find a swarm of cluster flies, flypaper and bug zappers aren't much use because these flies are not strong flyers. Contact the experts at Terminix®, who will control your infestation of cluster flies along with any other pests that may be bugging you.