Professional Cluster Fly Control Services in the UK

Cluster flies are often mistaken for houseflies, but they behave very differently. They are usually slower, slightly larger, and they become a problem mainly because they enter buildings in large numbers to hibernate over winter. While they are not known to spread disease, they can cause significant disruption through staining, odours, and repeated seasonal reappearance.

Why Cluster Flies Gather in Buildings

As temperatures drop in late summer and early autumn, adult cluster flies look for warm, dark, and undisturbed places. Lofts, roof voids, attics, and wall cavities are ideal overwintering sites — especially if entry points like vents, gaps under tiles, soffits, or cracks around the roofline are easy to access.

Common Signs of Cluster Flies

• Slow-moving flies gathering around upstairs windows or roof lights
• Large groups seen in loft spaces, eaves, or wall voids
• Dead flies collecting in corners, window sills, or behind insulation
• Staining on walls and window frames from fly activity

Do Cluster Flies Cause Harm?

Cluster flies are not considered a direct health risk. They do not usually breed indoors or feed on human food waste. However, heavy infestations can cause unpleasant odours, staining, and persistent nuisance behaviour — particularly when warmer spells bring them out of hibernation.

How We Control Cluster Flies

Because cluster flies hide in difficult-to-reach spaces, effective control needs the right approach:

• Inspection: Identify entry points and harbourage areas (often roof and loft related).
• Residual treatment: Apply professional-grade insecticides in key areas to reduce numbers and prevent reactivation.
• Prevention guidance: Advise on proofing, vent screening, and sealing likely access routes.

Best Time to Treat

Late summer to early autumn is the most effective time for preventative treatments — before the flies settle into loft spaces for winter. If you are already experiencing activity indoors, we can still treat and help reduce numbers, but prevention gives the strongest long-term result.

If cluster flies are returning seasonally, contact Shire Pest Solutions for a tailored treatment plan and long-term prevention advice.