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.


  • 3.5 mm x 6mm in size
  • Large reddish compound eyes
  • Thorax covered with yellow-gold hairs
  • Bristly yellow/black abdomen

Facts about cluster flies

  • Larvae tunnel into earthworms and develop inside them
  • Adult flies feed only on nectar
  • In late autumn they cluster together for hibernation in large numbers in roof spaces and lofts - this is how they got their name
  • If warmed up by artificial heat, flies will emerge prematurely
  • In early spring cluster flies will come out of hibernation


It is very difficult to prevent cluster flies from entering a roof/loft space, however, once the flies are inside control is fairly simple. Most household fly sprays will do the job, smoke formulated insecticides can also be used. Always read the label.

We do not treat cluster flies. You can find other professionals that are able to treat an infestation online or in a local directory.

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