Cluster Flies


These flies are commonly found throughout Europe and the UK. The name refers to their habit of clustering together in large numbers and hibernating in buildings. There are several species found in the UK but they are often found in mixed swarms. The sizes vary between species from 6 - 10mm. They are slightly larger than the house fly and appear to fly more sluggishly. Cluster flies can be recognised by their distinctive stripes behind the head, short golden hairs on their thorax and a mottled light/dark grey abdomen. Eggs are laid on damp soil or beneath dead and rotting leaves. The adult flies feed on the nectar of garden and wild flowers. As a free-living insect the length of the life cycle is weather dependent. In Britain two generations of cluster flies are common, but in hot summers up to four are possible. During the summer and early autumn cluster flies are rarely noticed as they are away from buildings. As the season cools they seek shelter in nooks and crannies in houses and other buildings.


What are the signs that you have cluster flies?

Cluster flies will start entering buildings during the autumn to escape the colder weather and to survive the winter. When the weather starts becoming warmer in the spring they will become more active again and will be more noticeable.

Cluster flies are usually found in rural or semi-rural areas and can be found in loft spaces or sometimes in unused rooms, or around sash windows. They are usually seen in large groups and will often be noticed around sunny windows.


Potential Harm

Cluster Flies are not known to carry diseases in this country. However large clusters of flies are often considered a nuisance.


What happens when a Cluster Fly treatment is carried out?

An appointment will be made for a pest technician to visit you at a suitable time. Access to loft spaces will be required. We have ladders that are able to access most domestic loft spaces.

The pest control technician will visit and assess the location of the cluster flies. Wearing protective clothing the technician will then set up ULV equipment which is a machine that will effectively disperse an insecticide into the area, usually the loft space. The length of time the machine is run will depend on the size of the loft space.

Following the treatment the cluster flies will become very active and will start to die very quickly, this starts within a few minutes of the treatment. The insecticide used will destroy that generation of cluster flies but it will not prevent them returning.



It is extremely difficult to prevent cluster flies entering a property. Fly proofing a building is not 100% effective. However, caulking around windows, and sealing obvious entry points can help.         

It has been observed that a single building in a row of apparently identical buildings will be selected for clustering year after year. This is no indication of poor hygiene standards and no explanation for the phenomenon has been found.


If you are experiencing regular cluster fly problems we are able to offer treatment to destroy the current cluster fly generation.