Richmondshire District Council

Information about cluster flies

Cluster flies are common in the UK and are so called because they hibernate in large numbers, or clusters, in buildings.

Swarming flies have a similar hibernating nature and these can form mixed populations of flies inside buildings.

Weather conditions in our country mean there are only usually two generations of cluster fly each year but up to four generations are possible in hot weather. 

In summer and early autumn, cluster flies are found in fields, but as the weather becomes cooler, they will find shelter in nooks and crannies in houses and other buildings and can often be found in large numbers (several thousand) in roof spaces.

Often, they will return to the same building year after year.

Large numbers of cluster flies hibernating together can produce a sickly smell and if warm enough will fly around living areas where they are attracted to the light. While this may cause a nuisance, cluster flies don't pose any risk to human health and their presence doesn't reflect poor hygiene.

Once inside the building, cluster flies don't breed. 

Our service

The standard treatment costs can be found on our domestic fees page.

This covers:

  • Initial visit and assessment
  • Advice on possible infestation cause and possible measures to deal with it
  • Treatment using pesticide

If no treatment is carried out, you'll only pay a call-out and survey fee.