get rid of cluster flies remove cluster flies treat cluster flies infestation

Pest control services for Berkshire, Hampshire, Oxfordshire, Buckinghamshire, Middlesex, Surrey & London. Established 1985.

PEST UK / Pests / Get Rid of Cluster Flies | Remove Cluster Flies

Get Rid of Cluster Flies | Remove Cluster Flies

What are cluster flies

Cluster flies look very similar to house flies. however they don’t buzz around and are typically sluggish. They gather in large numbers during late summer and early autumn whilst seeking sheltered places to hibernate during the winter. During the day they cluster on the sun-warmed walls of buildings. They eventually find their way inside to form clusters of many thousands in roof spaces, under tiles, in window sash boxes, around window frames, outside buildings and sheds.

Adult cluster flies emerge from hibernation in mid-spring and lay their eggs in the soil. When they hatch the maggot seeks an earthworm host and penetrates into its body and continues to develop until they become full-grown after two to three weeks. They subsequently emerge and reproduce. Up to four generations may be produced over the summer. Cluster flies and their descendants return to the previous hibernation site year after year.

There are a over 20 species of cluster fly in the UK; Pollenia rudis is the most common.

When do cluster flies become a nuisance

Cluster flies become a nuisance when they enter a building during the autumn to hibernate or when they start to emerge in spring or occasionally on warm winter days. You may want to get rid of cluster flies even though they aren’t a health hazard in the same way that house flies are. They only enter a building to hibernate, not to breed or feed.

How do I know if I have a problem with cluster flies

If you have a cluster fly problem or infestation you will notice dead, dying or lazy live flies around windows or in roof spaces. You may even see them sunning themselves on outside walls. You will only see them on warm winter days, in the spring and early autumn. Flies in the summer are likely to be house flies, bluebottles or other types of flies.

Cluster flies are generally most common in a rural environment. Heavily infested buildings may contain several thousand flies which can be a serious problem.

Treatment of cluster flies

Preventing cluster flies is not possible. Proofing a building may reduce the number of flies entering it but it’s unlikely to be 100% effective.

If you want to get rid of cluster flies PestUK will treat the infested and surrounding areas with the most modern insecticide sprays available, often in combination:

  • Effect Microtech CS which contains Permethrin
  • HSE Number 6287, made by Sorex or Permost Uni
  • HSE Number 6399 which contains Permethrin and Tetramethrin, made by Hockley International
  • K-Othrine WG250
  • HSE Number 5390 which contains deltamethrin 25%

Ficam D might also be used which contains an insecticide in a dust formulation @ 1% w/w Bendiocarb

A Coopex Smoke generator may be used, which contains Permethrin.

The type of insecticide used will depend on individual circumstances and be decided by the technician.

All these insecticides are biodegradable, almost odourless, non-tainting and do not corrode or stain. They are not highly toxic towards mammals but are extremely toxic to all forms of crawling and flying public health pests.

What do I do afterwards

After treatment, do not let domestic animals walk on treated surfaces until dry and if bare skin comes into contact with the treated surfaces while wet then wash. As long as the surfaces that have been treated were clean before treatment and are not washed down the insecticide will remain active for up to three months.


Dying flies may be seen in some numbers up to four weeks after treatment. Flies take time to die, how quickly depends on temperature and how much insecticide they have absorbed.

The treatment will not eliminate the fly infestation but kill the vast majority of flies present at the time of treatment. However there is a strong possibility that any survivors will build up their numbers to a nuisance level again in the following years as the hibernation site will be used year after year.


PESTUK are a member of the BPCA, the governing body for pest control in the UK. This provides assurance that PESTUK are an insured, trusted company with a team of professionally trained and qualified technicians who follow the BPCA Codes of Best Practice.

Call us on 0800 026 0308 or email us at for free local pest control advice or to book an appointment for pest control services near you.

PESTUK have offices across the south of the UK in Alton, Andover, East Grinstead, Farnham, Guildford, Maidenhead, Oxford and Wokingham

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