How To Get Rid Of Cluster Flies: Complete Guide

Cluster flies may seem harmless at first, but when they invade your home by the dozens — or hundreds — they quickly become a major headache. These slow-moving flies gather in attics, basements, and around sunny windows, creating a buzzing noise, staining surfaces, and causing frustration. The good news? You can take back control of your home with a combination of prevention, removal, and long-term control strategies.

This comprehensive guide will show you exactly how to get rid of cluster flies safely, effectively, and permanently.

What Are Cluster Flies and Why Are They in Your Home?

Cluster flies (Pollenia rudis) are often mistaken for common house flies, but they are slightly larger, darker, and move more slowly. Their name comes from their habit of “clustering” together in large groups when resting or overwintering.

Unlike house flies, cluster flies do not reproduce indoors. Instead, they spend the summer outside in the soil, laying eggs near earthworms. When fall arrives, they look for warm places to hibernate, and your home — especially your attic or wall voids — is the perfect shelter.

Where Do Cluster Flies Come From

Cluster flies start their life cycle as larvae that grow inside earthworms during the warm summer months. When they become adults, they look for cozy, protected spots inside homes and buildings to spend the winter. As spring arrives, they leave their hiding places, head outdoors, and lay eggs near earthworms to begin the cycle again. Once temperatures drop in the fall, the adult flies return indoors to find shelter all over again.

How To Identify Cluster Flies

Before you can eliminate them, you need to confirm you are dealing with cluster flies and not house flies or blowflies. Look for these key features:

• Size: Slightly larger than a house fly (about 8–10mm).

• Color: Dark gray body with golden hairs that give them a slightly shiny appearance.

• Behavior: Slow-moving, sluggish flyers that often gather on sunny windows or in groups in attics.

• Sound: A low, droning buzz compared to the high-pitched buzzing of house flies.

Correct identification is important because it helps you target the right treatment methods.

Signs of a Cluster Fly Infestation

Cluster flies are most noticeable during two times of year:

• Fall: When they enter your home seeking warmth.

• Spring: When they emerge from hiding places to go back outside.

Common signs include:

• Large numbers of flies in unused rooms or attics.

• Small dark specks (fly droppings) on windowsills and walls.

• Dead flies are accumulating in the window tracks.

• Buzzing sounds near ceiling lights or in the walls.

Spotting them early means you can prevent a major infestation.

How To Get Rid of Cluster Flies Naturally

If you want a chemical-free solution, these natural methods work well, especially for light infestations.

1. Vacuum Existing Flies

The simplest and fastest method is to vacuum them up. Use a shop vac or a strong household vacuum with a hose attachment. Be sure to empty the bag or canister outdoors immediately to prevent odor.

2. Essential Oil Repellents

Cluster flies dislike certain scents. Make a natural spray by mixing:

• 2 cups of water

• 10–15 drops of peppermint, eucalyptus, or lavender oil

Spray around windows, doors, attic spaces, and potential entry points. This will not kill flies but will deter them from gathering.

3. Keep Indoor Spaces Dark

Cluster flies are attracted to light. Keeping unused rooms dark during peak fly season can discourage them from gathering on windows.

Effective Chemical Treatments for Cluster Flies

If natural solutions are not enough, chemical control methods can eliminate cluster flies quickly and prevent them from coming back.

1. Residual Insecticides

Apply a residual insecticide around:

• Windows and doors

• Attic vents

• Baseboards and wall voids

Choose a product labeled for cluster flies and apply it in late summer or early fall to stop them before they enter your home.

2. Aerosol Space Sprays

For a heavy infestation in an attic or closed space, use an aerosol fogger or space spray. This knocks down active flies quickly. Always follow safety instructions and leave the area until it is safe to re-enter.

3. Fly Traps and UV Lights

Install UV light traps in attics, garages, or basements to continuously attract and trap flies over time. These are especially effective when combined with exclusion and sealing methods.

Sealing Your Home: The Most Important Step

No treatment is complete without stopping future infestations. Cluster flies return year after year unless you make your home less inviting.

• Caulk cracks and crevices around siding, windows, and doors.

• Install screens on attic vents and chimneys.

• Replace worn weather stripping on doors and windows.

• Seal gaps around utility lines, pipes, and cables.

Perform this inspection every late summer to ensure your home remains protected.

When to Call a Pest Control Professional

If you have a severe infestation or cannot find where the flies are getting in, a licensed pest control professional can help. They have access to professional-grade products and equipment that can reach wall voids and hidden spaces you might miss.

Professionals can also provide preventive treatments to stop future infestations.

10 Frequently Asked Questions About Cluster Flies

1. Are cluster flies dangerous?
No. They do not bite, sting, or spread disease. They are simply a nuisance.

2. Can cluster flies breed indoors?
No. Their life cycle depends on soil and earthworms, so they do not reproduce inside homes.

3. Why do they keep coming back every year?
Once they find a good hibernation site, they return year after year unless you seal their entry points.

4. What is the best time to treat for cluster flies?
Late summer or early fall is ideal. Treat before they enter to prevent large indoor populations.

5. Can I just kill them with a fly swatter?
Yes, but this is not practical for large numbers and does not stop more from coming in.

6. How long do cluster flies live indoors?
They can survive several months through winter, then leave in spring to return outdoors.

7. Are DIY solutions effective?
Yes, especially sealing and vacuuming. But heavy infestations may require professional treatment.

8. Will they harm pets or food?
No, they are not harmful to pets and do not infest food like house flies do.

9. Are cluster flies active at night?
No, they are generally inactive in the dark and most active during warm, sunny days.

10. What is the fastest way to get rid of them?
Vacuuming combined with residual sprays or fogging will provide the quickest results.

Long-Term Cluster Fly Prevention Tips

To make sure you never face another cluster fly invasion:

• Schedule annual inspections of your attic and siding.

• Treat your home’s exterior with a residual spray in late summer.

• Keep grass and landscaping trimmed back from the house.

• Seal every small gap, even those you think are too small — flies can fit through tiny spaces.

• Install tight-fitting screens and keep them in good condition.

Consistency is the key to keeping cluster flies out permanently.

Conclusion

Cluster flies may not be harmful, but they can be incredibly annoying and leave your home feeling dirty. The solution is a multi-step approach: remove existing flies, seal entry points, use natural or chemical controls, and maintain preventive measures year after year. By acting proactively — especially in late summer — you can stop them before they ever enter your home.

Taking these steps now will save you time, frustration, and ensure your living spaces stay clean, peaceful, and fly-free all year long.