Cluster flies are usually found in rural areas although they can be found throughout the UK.
Their name refers to their habit of hibernating in clusters, often in large numbers in the upper rooms and roof spaces of buildings during the autumn period.
Whilst there is a specific species of common cluster fly there are four other species which vary in size and colouration, so it is possible to have mixed populations of flies hibernating in suitable buildings. Cluster flies are not to be confused with House Flies or Bluebottles which are a health hazard
During the summer months these flies live and breed in fields. They are parasitic on earthworms and their larvae live in the soil, emerging as adults at the end of summer.
In the autumn, these flies congregate in large numbers on the outside of buildings, especially on sunny, south-east facing, light-coloured walls.
As the afternoon temperatures begin to fall they tend to crawl into crevices for shelter, sometimes through window frames, but mainly under the eaves/fascia boards into the roof space.
On warm days they may emerge and sun themselves but as temperatures drop they finally remain inside until the following spring.
The flies tend to return to the same property every year. It is not known why one building is preferred, it may be that the flies are attracted to lighter coloured buildings, sunnier spots, or use pheromones to locate old roosts. It has nothing to do with poor hygiene and the flies are not considered to be a health hazard.
They may become more of a nuisance if they escape into the house through the light fittings or similar holes in ceilings and gather in large numbers in sunny windows in an attempt to get outside.
There is very little that you can do to stop the flies getting in. Making sure that gaps around window frames are re-pointed and sealing obvious entry points can offer limited help, but it is not really possible to stop a fly getting into a loft and if one fly can get in, so can the hundreds of others.
Control of small infestations is fairly easy and using an ordinary aerosol fly spray in the loft will kill a large proportion of them, but will not penetrate into the cracks where flies may be hibernating.
If attempts fail contact us and they can be safely destroyed.