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What are Cluster Flies?

When fall arrives, bugs seem to disappear from our lives until spring returns. However, some bugs like to stick around throughout the winter months. Cluster flies have a habit of moving into homes to avoid the chilly winter weather. We’ve gathered information about cluster flies to help you identify and eliminate an infestation.

What Do Cluster Flies Look Like?

Cluster fly

Cluster flies are similar in appearance to house flies, but slightly larger. They grow between 8-10mm in length. Cluster flies have a dark gray or black body with small, golden hairs on their thorax. A checkered pattern can be seen on a cluster fly’s abdomen, which helps separate them from other flies. These flies have a pair of translucent wings that overlap when resting. Like other flies, they have two large eyes.

Why Are Cluster Flies in My Home in Winter?


When temperatures begin to drop, cluster flies gather on the exterior of homes and buildings. Toward the end of fall, these flies try to move inside in search of a safe place to overwinter. They will spend the winter in your home. They prefer areas that are dark and protected like wall voids and attics, which is why they’re sometimes referred to as attic flies. Once spring arrives, they head outdoors. You may notice them emerging from their hiding spots. On warm winter days, these flies may be tricked into coming out early.

What Do Cluster Flies Eat?

Cluster fly on leaf

Adult cluster flies feed on nectar from plants. The larvae feed on their earthworm host. Instead of breeding indoors, they lay eggs in the soil where larvae can easily find earthworms.

Are Cluster Flies Dangerous?

 Cluster fly on cup

Cluster flies don’t bite humans, but you don’t want to let these flies hang out in your home. When cluster flies find a safe and warm location to overwinter, they release a pheromone that attracts other flies to the area. This results in large numbers of cluster flies gathering near or in your home. Though they are inactive in the winter, they will emerge when temperatures rise. Since they prefer hidden locations, eliminating them can be difficult. This also presents a problem if they die and can’t be removed from your home. Dead cluster flies attract beetles and carpenter ants. Their feces can also leave dark stains on walls and windows.

What Are Signs of a Cluster Fly Infestation?


When pests invade homes, they often leave behind clues that can alert you to their presence. Here are a few signs that you’re dealing with a cluster fly problem.

  • Cluster Flies on Your Home’s Exterior: This is one of the main signs of an infestation. Cluster flies gather on windows where there’s sunlight to keep them warm. You’ll often spot them here before they move inside.
  • Cluster Flies in Your Home: You may notice a few flies buzzing around inside. There’s a good chance others are hiding nearby. These flies will move slower than other flies.
  • Buzzing Noise: When multiple cluster flies are in the same location, their buzzing noise can be heard.
  • Cluster Fly Droppings: Small, black spots on windows or walls could be a sign of an infestation. This excrement can stain walls, furniture, and fabric.
  • Sweet Odor: Cluster flies release a sweet odor when disturbed or crushed.

How to Prevent Cluster Flies

Sealing window with caulk gun

Keeping cluster flies out of your home begins with preventative measures. Check out a few ways to avoid these bugs.

  • Seal Cracks & Gaps: Cluster flies can slip into small spaces. Check for and seal any holes you find. Examine common entry points like doors, windows, and electrical outlets.
  • Check Door & Window Screens: A tear in screens can provide cluster flies with easy entry to your house. Repair or replace damaged door and window screens.
  • Create a Protective Barrier: Using a plant-based insecticide spray that kills on contact and provides residual repellency, like our Yard Bug Spray, can help keep bugs out. The residual repellency acts as a barrier and deters pests from entering your home. Spray your yard in September to mid-October for best results.

How to Get Rid of Cluster Flies

Home Bug Spray & Flying Insect Killer

Sometimes cluster flies ignore no vacancy signs and sneak inside homes. If this happens, there are things you can do to eliminate an infestation.

  • Sweep & Vacuum: If you find dead flies, you’ll want to remove them. This will help prevent other pests from being attracted to your home. Make sure to discard them outside, away from your house.
  • Use a Plant-Based Insecticide Spray: Our Home Bug Spray and Flying Insect Killer will kill cluster flies when directly sprayed. The residual repellency will help keep cluster flies from returning.

Cluster flies may want to hideout in your home, but that doesn’t mean you have to let them. Eliminating entry points and taking other preventative measures can help keep your home cluster fly-free. If you’re dealing with a pest problem, we want to help! Check out our Maggie’s Farm Simply Effective Pest Control products.

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