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Why do cluster flies get into properties and what can be done?
Table of contents:
I was called out to a customer who said there had been a serious fly infestation in her kitchen. When I visited and saw a handful I was fairly sure it was a Housefly but just to be sure collected a sample and sent it away for analysis. My contact said he also initially thought Housefly, but got an entomologist to provide a second opinion. The identification came back as Cluster Fly.
Why Do They Get In?
Cluster Flies have external breeding sites and there is no known way that they can be completely eradicated.
As the temperature begins to drop in autumn they venture into properties through small cracks and crevices, soffits, under tiles, and through the seams of windows.
Once inside a property, they tend to gather in loft spaces, ceiling, or wall voids where it's quiet and warm in order to hibernate over the winter months. They come out in spring but this can be earlier with the warmth of houses causing a premature emergence and the subsequent blight to the occupants.
They live outside in warmer months and the females lay eggs in soil. The larvae parasite earthworms with adults emerging to continue the cycle.
This is why identification of the insect is so important. Unfortunately as you perhaps can understand from the explanation above, the occurrence of Cluster Flies is a situation that cannot be easily resolved. Other common fly infestations in properties can be solved by sorting out hygiene issues, drain problems, clearance of organic matter etc.
However, there are a number of actions that can help at those points in the year when they make their presence felt.
Methods of control (short term)
Heavy infestation
Pest control technicians can perform space treatments to knockdown the infestation. This will provide some immediate relief, although this will require a large clean up operation with a vacuum cleaner.
Lighter infestation
The vacuum cleaner is a useful tool for fly removal and cheap insect aerosols can do a job in reducing numbers.
Methods of control (long term)
Treatment Programme
"Treatment for Cluster Flies should never be approached as a quick easy fix. In many cases, the problem will reoccur several times over the winter months, and then potentially year on year. By offering customers a solution to rid the property completely of cluster flies you could potentially be setting yourself up for a fall.
A possible approach would be to offer a Treatment Programme consisting of 4 visits between early Autumn and late Spring, rather than a one-off treatment. The treatment would start with an inspection of the loft/ attic area in order to establish whether there are any bats present. If found to be present, the best course of action is to contact the Bats Trust. It is also prudent to make sure that any water storage tanks are completely covered before treatment commences to prevent any potential contamination." - Matt Towler (LodiUK)
The treatment would involve the use of a powerful insecticide that knocks down, but also provides a strong residual for up to 12 weeks.
Electric fly killers
Most EFKs are not suitable for cluster flies, but there is one available that has been designed to collect larger numbers (click link below for more information):
A cheaper option for controlling lower numbers is a glueboard fly machine (click link below for more information):
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