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Cluster Flies

Cluster Fly Control: Protect Your Home or Business

Picture of Cluster Fly on Leaf


  • Clumsy and slow, cluster flies often collide with lights and windows before dropping to the ground and struggling to get back up.
  • During colder months, you may find these pests hibernating inside of attics or in wall voids.
  • Cluster fly larvae burrow into earthworms and feed on them until the adult emerges several days later.


About half an inch long and slightly larger than a house fly, cluster flies are dull gray with yellow hairs, reddish-orange eyes, and translucent wings. This pest lays its eggs in the soil, so it’s unlikely that you’ll see them. Maggots are cream-colored and live inside of their earthworm hosts until they mature.

How Do Cluster Flies Get Inside Buildings?

When the days get cooler, cluster flies swarm the sunny sides of houses in search of a spot to overwinter. Attracted to the protection of heated environments, they may crawl in through torn screens, open doors, or cracks around exteriors.

Cluster flies seek out warm buildings, leaving most businesses vulnerable. They often enter hotels, doctor’s offices, and other facilities where people come and go frequently. Retailers that sell fishing bait are also at risk since the larvae have a parasitic relationship with earthworms.

Signs of A Cluster Fly Infestation

  • Numbers – You might see large groups of these pests flying indoors and swarming windows.
  • Spots – Small, black spots on glass and walls could be cluster fly waste.
  • Sightings – These insects are most active when temperatures rise, so if you see them on a warmer day, they’re probably hibernating nearby.
  • Sluggish – Cluster flies move more slowly than other species, making them easy to swat or capture.

Problems Caused by Cluster Flies

Primarily a nuisance, cluster flies don’t carry any diseases. Though harmless, they can be annoying when they swarm and buzz. They also tend to return to the same location to hibernate, so there’s a chance you’ll experience repeat infestations.

Although cluster flies aren’t associated with filth, they do look similar to insects that are. Customers in restaurants and grocery stores may assume that these pests are a sign that the business is unclean. This can result in costly losses in sales if left unchecked.

Prevention Tips

Cluster flies come into homes and businesses looking for a warm place to hide. The best way to keep them out is to block their entry. Repair or replace damaged screens and seal cracks around doors, siding, and windows. If problems persist, contact the professionals at Western Pest Services for expert help.

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