Cluster Flies

Cluster Flies Fact Sheet


There are four main species of fly collectively known as cluster flies.  They are:

The Autumn Fly (Musca autumalis) - a small fly of about the same size and colour as the housefly, but with a yellow abdomen.

The Common Cluster Fly (Pollenia rudis) - a larger fly of a dull, dark, dusty brown/grey colour with a “tessellated” abdomen.

The Green Cluster Fly (Dasyhora caynella) - about the same size as a housefly, shiny green/blue in colour.

The Yellow Swarming Fly (Thaumatomya notata) a smaller species of hibernating fly, yellowish body/black markings, sometimes confused with the fruit fly.

Biology and Habitat

Cluster flies are very common; the adult flies hibernate during the winter months in roof spaces of houses and/or farm buildings.  After this time the flies lay their eggs in the earth and/or animal dung.  As the soil temperature increases in late spring, the eggs will hatch.  The larval stage is parasitic, entering earthworms and feeding upon them until emerging as an adult fly.  There may be two to four generations of flies in a single year.

The common cluster fly prefers a warm wet summer, whereas the autumn fly prefers dryer, hotter conditions.

Cluster flies migrate from the outside conditions into the lofts of house and/or farm buildings during the winter months.  Obvious signs of an infestation include large quantities of lethargic/dead flies around windows.  Once in the roof spaces the flies will stay in hibernation until the spring.


There is no risk to public health.

Cluster flies do not damage property; they will die and become very unsightly if they do not successfully hibernate.

Water tanks in the loft spaces should be covered.

Cluster flies are not to be associated with dead animal bodies or faeces and there are no maggots.


Cluster flies emit a clustering pheromone that encourages them to hibernate together and for subsequent generation to follow to the same property.

For small infestations around windows and behind curtains, they can be removed with the use of a vacuum cleaner.  For large infestation in loft spaces, treatment is best carried out after the first frosts of winter; this usually ensures that all of the hibernating flies are in the treatment area.  The treatment best designed at this time is to treat with an insecticide space spray, Ultra Low Volume application through a Micro-Gen machine, will quickly knock down any flies present.

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