Pest Advice - Cluster Flies

What are they?

cluster fly

Cluster flies are common in the UK and are so called as 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.

Due to weather conditions in our country, there are only usually 2 generations of cluster fly each year but up to 4 generations is 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. Whilst this may cause a nuisance, cluster flies do not pose any risk to human health and their presence does not reflect poor hygiene.

Can I treat them? 

It is best to try to prevent the flies access into buildings by blocking access into cavity walls e.g. replace missing bricks and seal around windows and doors.

Once inside the building cluster flies do not breed and can be controlled by using a wide range of insecticides*, pesticides* and fly strips* which can be purchased from garden centres, hardware and ironmongers and DIY stores.

You should always survey the area for bats which are protected by law before applying treatment and contact Natural England Tel no: 0845 1300 228

*Always refer to the product instructions BEFORE use and follow these at ALL times.



Last Updated on Wednesday, May 8, 2024