Cluster Flies

The Cluster Fly is often mistaken for the common house fly but they are more sluggish and often appear to fly very slowly. They can overwinter in vast numbers in lofts, cellars and dark voids. These flies are of no particular harm but can be alarming because of their great numbers. Generally noticed on the first warm days of spring when they congregate on the inside of windows. Frequently found in window frames, particularly sash windows. Interesting life cycle - lay eggs in damp earth and resulting larvae migrate into the bodies of earthworms where they develop into maggots which then bore out of the worm to pupate. Easily controlled with spray, fumer or electronic device.

Where are they found?

Cluster flies tend to overwinter in lofts, cavity walls, cellars and other enclosed dark voids. There they can accumulate in very large numbers and subsequently appear with the first warm sunny days of spring.

They are usually first noticed at the windows or in conservatories as quite large, sluggish, dark coloured flies. Most simply exit the building the way they came in and go un-noticed by us. In some cases many hundreds can find their way into rooms through ill-fitting window frames and especially so in the case of sash windows.