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Facts About Cluster Flies

When fall comes around, you may find cluster flies (Pollenia) buzzing around your home. These pests enter houses seeking shelter and warmth during winter. When temperatures rise in spring, cluster flies emerge. We’ve gathered information about cluster flies to help you keep these pests from spending the winter in your home.

What Do Cluster Flies Look Like?

Cluster fly

Adult cluster flies are dark gray and about 1/3"- 2/5" in length. They have golden hairs on their body with a prominent light and dark checkered pattern along their abdomens. You can also spot a striped pattern behind their head. They have two large eyes, like other fly species. Cluster fly larvae look like tiny, white worms.

Cluster Flies vs. House Flies

Cluster flies are often confused with house flies because they look similar. However, there are ways to tell them apart. Cluster flies are slightly larger and have wings that overlap when resting. They also move slower than house flies. Unlike house flies, cluster flies gather in large groups in sunny locations.

Types of flies

Where do Cluster Flies Live?

When cluster flies head inside, they gravitate to the highest parts of your house, like your attic. This is why they’re sometimes called attic flies. They hide in cracks, crevices, and voids. In your home, cluster flies are found behind curtains, underneath clothing in closets, behind picture frames, and furniture. These flies are found mostly in Europe, North America, Australia, and New Zealand. They stay in proximity to humans.

Cluster Fly Habits

Cluster flies belong to the same family as blow flies. Outdoors, they prefer to live close to the ground. They’re sometimes called grass flies. Adults feed on flower nectar, plant sap, fruits, and other organic material. Their larvae are parasites of earthworms. Female cluster flies lay eggs in the soil near earthworm burrows. This allows the larvae to burrow into the ground and feed on the worms.

What Causes Cluster Flies in the House?

Lit light bulb

Cluster flies are attracted to light, which explains their fixation with windows on sunny days. They are also attracted to artificial lights at night. These flies are not attracted to garbage and other refuse like so many other types of filth flies.

Cluster Flies in Summer

During the summer, cluster flies prefer to be outside. They spend the spring and summer months breeding. Cluster flies lay eggs in the spring and summer. When the larvae hatch, they feed on earthworms. You may still encounter a few cluster flies during warmer months when they become active. If these flies spent the winter in your home, they will emerge in your house looking for a way outside.

Cluster Flies in Winter

Cluster flies are an overwintering pest, which means they seek shelter to escape cold weather. When temperatures drop, cluster flies look for a warm and safe place to hide. They first gather on the sides of homes before slipping indoors. They head to dark areas including attics and wall voids. Once the cold weather passes, these pests emerge in homes trying to get back outside.

Are Cluster Flies Dangerous?

Cluster fly on leaf

Though cluster flies are considered a nuisance as overwintering pests, they do not bite humans or animals (other than earthworms), and they do not spread bacteria or lay eggs in food. They pose no health threat whatsoever. Cluster flies are problematic because of the size of the infestation. Since they cluster together, infestations can become large.

The Cluster Fly Life Cycle 

Generally speaking, each season brings with it around three to four generations of these flies.

Once adult cluster flies emerge from overwintering in the spring, they lay eggs in cracks in the soil—these eggs hatch within about 3-4 days and the larvae proceed to feed on earthworms for two to three weeks.   

The larvae will then pupate in the soil for 11-14 days, after which a new generation of adult cluster flies emerge. From egg to death, the cluster fly lifespan lasts from one to three months. 

Will Cluster Flies Eventually Go Away on Their Own?

If cluster flies have made it into your home in the fall to overwinter, they will usually stay out of the way. Occasionally, they emerge on warmer, sunny winter days, attempting to get outside through your windows. They lethargically float around in a zombie-like state, and sometimes just fall to the floor like they're dead. At any point, cluster flies can appear to be half-dead or dead, but, like zombies, they never quite go away if left alone. 

How to Prevent & Control Cluster Flies in Your House

Flying Insect Killer

Before cluster flies arrive, you’ll want to pest-proof your house. These preventative measures can help to keep cluster flies out of your home.

  • Make sure door and window screens are in good repair.
  • Seal cracks, crevices, and holes around the outside of your house and screen plumbing/cable penetration points.
  • Spot treating for cluster flies outdoors during the summer with a plant-based Flying Insect Killer will help reduce their populations. This will help prevent them from coming inside in the fall to overwinter.

How to Get Rid of Cluster Flies Naturally

Yard Bug Spray & Home Bug Spray

Cluster flies are quite harmless outdoors, and you will mostly have to deal with their nuisance existence indoors. However, outdoor prevention steps always help mitigate indoor pest problems. Here are a few tips to help get rid of cluster flies.

  • Create a Protective Barrier: Spraying the perimeter of your yard with a plant-based insecticide spray can help keep cluster flies away. Our Yard Bug Spray kills bugs on contact, while creating a protective barrier that repels pests.
  • Interior Treatment: Our Home Bug Spray and Flying Insect Killer kill pests on contact. They also will provide you with residual repellency. They are formulated with plant essential oils making them a more environmentally and family-friendly option.
  • Vacuum or Sweep Flies: If you find dead cluster flies, you’ll want to vacuum or sweep them up. This will prevent other pests from showing up who are attracted to them.
  • Implement Preventative Measures: To ensure you don’t have a returning cluster fly problem, you’ll want to implement the above preventative measures. Sealing entry points will make it harder for cluster flies to bug you.

Always carefully follow any directions on pest control product labels, including for storage and disposal.


How do you control Cluster flies in your home and yard? Leave us a comment! We want to hear your tips and tricks! 


For scientifically-tested, effective fly control in your home that is friendly to the environment, try Maggie’s Farm pest control products. Our promise is that our plant and mineral-based products are developed by scientists and seasoned pest control professionals to be the most effective.

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