What are Cluster Flies?

Cluster flies are large, slow-moving insects that often become a problem inside homes and buildings during cooler months. Unlike houseflies, cluster flies do not breed in garbage or food waste. Instead, they develop outdoors in soil where earthworms are present. In late summer and fall, they look for warm places to overwinter and often enter attics, wall voids, and upper rooms of homes. While they are not dangerous to humans, their habit of gathering in large numbers indoors makes them a frustrating pest.

Signs of Cluster Fly Infestation

You may have cluster flies if you notice:

• Large numbers of flies gathering near sunny windows or in upper rooms
• Slow-moving flies that appear drowsy compared to houseflies
• Dead flies collecting around windowsills, attics, or light fixtures
• A recurring presence of flies each fall and winter season
• Buzzing sounds in walls or ceilings on warmer days

Why They are a Problem

Cluster flies do not spread disease in the same way as houseflies, but they still cause significant annoyance. When they gather indoors in large numbers, they leave behind droppings and dead bodies that attract other pests such as beetles and mites. Their presence can create an unpleasant environment for homeowners and can be particularly disruptive in office buildings, schools, and businesses where appearance and sanitation are important.

Where Do They Come From?

Cluster flies originate outdoors and breed in soil where earthworms live. As temperatures cool in late summer and fall, they look for sheltered places to overwinter. Common entry points include:

• Gaps around windows and doors
• Attic vents and soffits
• Cracks in siding, brickwork, or roofing
• Open chimneys or other structural openings

Once inside, they gather in wall voids, attics, and upper floors until spring, when they try to exit the building.

How to Get Rid of Cluster Flies at Home

If you are wondering how to get rid of cluster flies, here are a few steps you can take:

• Seal cracks and gaps around windows, doors, and siding with caulking
• Install fine mesh screens over vents and chimneys
• Use a vacuum to remove visible flies indoors without crushing them, as this can leave stains
• Keep attic and upper rooms well-sealed to reduce entry points
• Reduce outdoor lighting at night that may attract flies toward the house

These measures can help reduce infestations, but cluster flies often return year after year unless preventative treatments are applied.

Cluster Flies vs Houseflies

Cluster flies are commonly mistaken for houseflies, but there are key differences:

• Cluster flies are slightly larger, slower, and darker with golden hairs on their thorax
• Houseflies are faster, more active, and breed in decaying organic matter, unlike cluster flies
• Cluster flies typically appear in late summer and fall, while houseflies are active throughout the warmer months
• Cluster flies tend to gather in large groups indoors, while houseflies are more likely to be found around food and garbage

How We Can Help

At Go Away Pest & Wildlife Control, we provide targeted solutions to prevent and eliminate cluster fly infestations. Our team identifies entry points, applies safe treatments to reduce overwintering populations, and offers long-term prevention strategies to keep your home or business fly-free. With professional care, you can avoid the yearly cycle of cluster flies and enjoy a cleaner, more comfortable space.