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Pest Library · Seasonal invadersCluster Flies Identification Guide
How to identify cluster flies, the sluggish flies that appear in attics and windows every fall and winter.
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How to identify
What cluster flies look like
Cluster flies are slightly larger than house flies, dark grey with golden hairs on the thorax. They are slow and clumsy indoors.
They gather on sunny walls in fall, then crawl into walls and attics to spend the winter.
Signs you have cluster flies
- Many slow flies on south and west facing windows
- Dead flies on window sills and in attics
- Flies appearing indoors on sunny winter days
Are they dangerous?
Cluster flies do not breed indoors or spread disease, but large numbers are a real nuisance and can stain walls and windows.
How to prevent them
- Seal gaps around windows, siding, soffits and vents in summer
- Repair screens
- Book an exterior treatment in late summer, before they move in
Quick facts
Scientific namePollenia spp.
Size8–10 mm
ColourDark grey, golden hairs on thorax
Most activeFall and warm winter days
Found inAttics, upper floors, windows
Risk levelLow (nuisance)
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