Cluster Flies


Cluster Fly Control


Cluster fly treatments starting from £65.00

(Prices vary on the size of the property)

Have you noticed increased levels of fly activity around the house? Especially around south facing windows? The chances are these could be cluster flies.



Bentley Environmental 3 best rated in Winchester award 2019


 We have been listed as one of the Top 3 Pest control companies in Winchester for a third year running.
We have reached this position by providing consistent high quality service in our area of business.


Office phone01962 277020

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Cluster flies are found throughout Europe and the UK. They are harmless, and do not carry any diseases that affect humans so they pose no health issues.

Cluster flies get their name due to their habit of clustering together in large numbers to over winter. There are several species found in the UK, and they can be found in mixed swarms. These sizes vary between species to species ranging from 3 to 8mm in length. Only the adult flies over winter, these start to cluster from September and onwards.

Once the flies have found a suitable site to hibernate for the colder months they emit a pheromone which attracts other flies. Often its possible you can smell their pheromone when large numbers of the flies are together, this is a sickly sweet smell. They will return year after year to the same site in ever increasing numbers, which is why it’s important to carry out treatment for the cluster flies.

They emerge in early spring congregating on walls, roofs, fences, and trees etc. to warm up in the sunshine. They then fly off to lay their eggs, these are usually laid in turf, leaf litter, compost heaps, or even muck heaps. Once hatched the larva which are parasitic seek out earthworms, they then bore through the worms skin and proceed to eat it alive. When the worm dies the larvae emerge and pupate in the surrounding soil, the adult flies feed on the nectar of garden and wild flowers. During the summer, cluster flies don’t tend to be a nuisance, only as the autumn approaches do they become a pest as they start to invade peoples house’s and offices.

Cluster flies look for a warm place to hibernate throughout the winter months, homes in rural areas are usually more susceptible to infestation. They usually cluster within roof spaces and window frames or any other spaces they find suitable.





To treat a cluster fly infestation we carry out loft/roof space treatments with either an insecticidal aerosol total release spray or with fogging/ULV (Ultra Low Volume) equipment. This kills the flies within the loft and will help to reduce the numbers of flies in and around the property dramatically.

We also carry out treatments to internal and external window frames, where we apply a residual insecticide. The flies land on the window casings and absorb the insecticide through their body when they come into contact with the insecticide.
In extreme cases, we can also apply external treatments to window frames, walls and soffits and fascias. Although the treatments have to be timed well as bad weather can wash the treatment away instantly!

The amount of treatments for Cluster fly infestations can vary. We have customers that need a single treatment, or a single treatment each year until numbers are drastically reduced. A heavy infestation of flies can take several treatments over the course of a few years to eradicate the cluster fly population completely. 

It is rarely possible to totally proof a building to prevent the flies from gaining entry. Sealing window frames, sky lights etc. will help along with any other potential entry exit points.




We also supply and install Electronic Fly Killers (EFK’s) for our customers. A popular location for installation is in kitchens and in conservatories. This deals with Cluster Flies in the season, but also deals with any other flies and insects, such as moths and wasps that enter into the house through open doors and windows. It just offers some reassurance for fly control all year round.
We can supply and install the more common commercial looking EFK, or we have a range of domestic units designed to be discreet and blend in to the home.

Please note that we can only install the EFK’s to a nearby plug socket (within 1 meter).
In some cases an electrician sourced by the customer would be required to install new electrical points.






Frequently Asked Questions

“Are the treatments safe to carry out with people in the house?”
Yes. We only carry out an insecticidal space spray to loft areas of properties, which remains within the loft. After treatment, do not enter the loft for 48 hours.

“What happens to the flies after the treatment has been carried out?”
Once the treatment has been carried out the flies will die within the loft space and fall onto either the boarding or loft insulation. After a 48 hour period the loft can be re-entered and the flies swept away or hoovered up. For an additional fee we can return to carry this work out for you.

Will one treatment solve my fly problem?
If you are lucky then you may only require one treatment, this is rare with cluster fly infestations. If you have had a fly problem over a period of time, 2-5 years for example, then it is very likely that you will need several treatments to eliminate the problem. So it is best to treat for cluster flies as soon as you identify you have a problem.

When is the best time to treat cluster flies?
Treatments are most effective in spring and in autumn time.

I have bats in my loft, can I treat the cluster flies in my loft?
If you have bats in your loft then no we are not allowed to carry out a cluster fly treatment. In Britain all bat species and their roosts are legally protected, by both domestic and international legislation. You can read more information on this by clicking here.


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