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.

How to Prevent Entry

In most cases it is very difficult to prevent cluster flies entering your buildings as they can gain access through the tinest of cracks. It might be worth at last looking for obvious entrance points but realistically these may be dificult to find and seal.

Not every year is bad for cluster flies so treating them when present is often the best option available.

Be aware that bats may be using your loft as a winter roost or a summer breeding site and that it is illegal to disturb bat roosts. Blocking acces to cluster flies may also block access to bats and, given that the only time to proof against cluster flies is during the summer when they are living outside, blocking holes may also trap nursing bats and their young in your loft where they may then die.