Flies in winter? Look up.
Those slow flies on a sunny window likely spent the cold months tucked in your attic or walls.
They move in for fall.
Cluster flies gather on warm, sunny walls in fall and slip into gaps to overwinter.
They wake up early.
Warm days in late winter draw them out toward light and windows.
Seal before fall.
Closing gaps around siding, vents and windows keeps next year’s flies outside.
Cluster flies are slow, large flies that spend winter hiding in attics and wall voids. On warm days in late winter and early spring, they crawl out and gather on sunny windows, often in upstairs rooms.
They don’t breed in your house or your trash. Sealing the outside before fall matters most, and it pairs well with quarterly pest control that keeps an eye on entry points year round.
How do you identify cluster flies?
Cluster flies are a little bigger than a house fly, dark gray, and move slowly. Look for golden hairs on the back and wings that overlap when they rest.
They act sluggish and clumsy, buzzing against glass or circling light fixtures. House flies are quicker and show up around food and garbage, not empty upstairs rooms.
Why are cluster flies in my house in winter?
Cluster flies come inside in fall to survive the cold, not to feed or breed. They gather on warm, sunny walls, then squeeze through gaps around siding, soffits, vents and windows.
Once inside, they rest in attics and wall voids. A warm winter day or the furnace kicking on wakes some of them, and they follow the light into your rooms. That’s why you can see flies in January with no open door in sight.
Outdoors, their young develop in soil and feed on earthworms. So homes near lawns, fields and open ground in Kansas City see more of them.
How do you get rid of cluster flies?
For flies already inside, vacuum them up. They’re slow, so a vacuum with a hose is the fastest, cleanest fix.
Don’t crush them on walls or curtains, since they can leave a stain. Swatters and sticky traps catch a few but won’t reach the ones hiding in your walls.
How do you keep cluster flies out next year?
The best time to stop cluster flies is late summer, before they move in. Seal gaps where they enter:
- Caulk cracks around window and door frames
- Repair torn screens and gable vent screens
- Seal gaps at soffits, fascia and siding joints
- Close openings where pipes and wires enter
Our pest-proof your home checklist walks through each spot. Read pest control in winter for what we do in the cold months, including dusting exterior overwintering spots when it’s too cold to spray. Coverage for cluster flies depends on the situation, so call 913-735-5451 and we’ll tell you what fits your home.
Cluster flies come in with other occasional invaders, like Asian lady beetles and stink bugs in winter.
Seeing flies on sunny windows every winter? Call 913-735-5451, answered 24/7, or schedule online. Most services can be scheduled same day.
Frequently Asked Questions
Cluster flies don’t bite, sting or carry disease from your trash the way house flies can. They’re a nuisance, and a large group can leave stains or a musty smell.
Cluster flies come from outdoor soil, where their young feed on earthworms. Adults move into attics and walls in fall to spend the winter.
Cluster flies wake on warm days and move toward light and heat. South and west windows in upstairs rooms often get the most.
No, cluster flies don’t breed indoors. The flies you see in winter moved in during fall and are waiting for spring.
Seal gaps at soffits, fascia, siding joints and attic vents before fall, when cluster flies look for a place to spend the winter. Repairing torn vent and window screens helps too.
