Why Do I Have Cluster Flies in My Seattle House?

Author: Kurt Treftz, Cascade Pest Control
cluster fly

Are you finding flies in your home during the colder winter months? Then you might be facing a cluster fly invasion. Unlike regular house flies which are not active during the winter, cluster flies become a nuisance with the lack of warmth and sun in the winter months in Washington state. 

If you see an unusually large number of flies settling on the exterior of your Seattle home or emerging inside your home, take action.

Image credit: Wikipedia

What are Cluster Flies?

Cluster flies are a type of fly known for their clustering behavior (hence their name). They tend to gather together in large groups especially as the weather cools. They are slightly larger than a typical house fly with a gray body covered in yellow hair so that they almost seem golden in the right light. 

They can also be distinguished from the house fly by their sluggish motion. They don’t move nearly as quickly as their cousins. 

Why do Cluster Flies Target my House?

Believe it or not, they aren’t specifically targeting your home. These flies actually prefer to live outdoors (eating rotten food, rubbish, manure, and animal waste and laying their eggs in earthworms). This is why they aren’t nearly as much of a problem in the summer. 

Most cluster flies enter your home accidentally in the late fall and winter as they search for a place to overwinter / hibernate. They want a sheltered place and your home provides it. They will often rest in large numbers on the sunny side of homes and buildings and then slip in as they find an opportunity. 

They will often find sanctuary in your attic, especially if there is a light bulb or other light source to attract them. They will swarm around it and find their way into your home.

Are Cluster Flies Dangerous?

Cluster flies do not bite or carry diseases known to be harmful to humans. They are mostly considered nuisance pests. And rightfully so, who wants to deal with dead flies dropping from the ceiling or buzzing incessantly in and around your home? They can also leave dark spots of excrement on windows, walls, and sills. 

cluster flies

Image Credit: University of New Hampshire

How do I Prevent Cluster Flies?

Like many other pest issues, the best offense is a good defense. Take steps early to prevent an infestation. Most cluster fly crimes are ones of opportunity. Remove the temptation and these flies are not likely to target your home. 

Preventative Steps:

  • Exam the outside of your home and seal up any cracks, openings, etc that can be a gateway for pests.
  • Make sure screens are in good order
  • Ensure that vents are covered and intersections of roof sections and chimney are sealed.
  • Eliminate any standing water outside your home that attracts pests to breed
  • Turn off exterior lights that can lure in pests
  • Vacuum up (don’t squash) flies to prevent leaving behind marks. 

But, if you do find yourself struggling with a swarm of cluster flies, give Cascade Pest Control a call: 888-989-8979.

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