Cluster Flies treatment in Chicago
Sluggish flies that overwinter in wall voids and attics, then appear indoors on warm days.
Cluster flies are slightly larger and noticeably slower than house flies, with golden hairs on the thorax. They are an autumn and late-winter problem more than a summer one.
In autumn they gather on warm, sun-facing walls — usually the south and west sides — and work their way in through gaps around windows, soffits, siding and roof lines. They then overwinter, dormant, inside wall voids and attics.
The confusing part for homeowners is the timing. On a mild winter day or the first warm stretch of spring, the warmth wakes them and they emerge into living space, seemingly from nowhere, clustering at windows. There is no food source indoors and no sanitation failure — they are simply waking up on the wrong side of the wall.
The durable fix is exclusion combined with a properly timed exterior treatment in early autumn, before they move in. Treating in February deals with what you can see; treating in September deals with next February.
Signs you have cluster flies
- Slow, clumsy flies at windows on warm winter and spring days
- Large numbers massing on sunny exterior walls in autumn
- Clusters in attics, upper rooms and unused spaces
- Dead flies accumulating on window sills
How we treat them
- Exterior treatment timed to late summer / early autumn entry
- Sealing of soffit, siding, window and roof-line gaps
- Attic and void treatment where flies are already established
- Removal of accumulated dead flies, which attract secondary pests
Common questions
Why do they appear in the middle of winter?
They are overwintering inside the structure. A warm day raises the temperature in the wall void or attic enough to wake them, and they head towards light — which puts them in your living room.
When is the best time to treat?
Late summer to early autumn, before they move in for the winter. That is the treatment that actually changes next year.
Other pests we treat
Dealing with cluster flies?
Free site estimate anywhere in Chicagoland. See a pest within 2 weeks of our service and we come back free.