Wednesday, June 19, 2024

Cluster Flies In Your House?

November 8, 2012 by  
Filed under Home Maintenance, Pest Control

During the summer months these flies live and breed in grassy fields and are seldom noticed. In the autumn they would, under natural conditions, hibernate in dry sheltered areas such as under loose bark or in hollow trees. The survivors of the winter would then emerge the following spring to return to the grassy fields to continue their life cycle.

However, with the encroachment of housing onto green field sites bordering pasture land it is quite common in the autumn for these flies to collect in large numbers on the outside of buildings, especially on sunny, light coloured walls. As the night time temperatures begin to fall they tend to crawl into crevices for shelter, sometimes through ill fitting windows and frames, but mainly under the eaves/fascia boards into the roof space.
The following days they may emerge and sun themselves but finally they remain inside until the process is reversed the following spring.
These flies may then be discovered when you enter your attic (to retrieve your Christmas decorations?). Your attic light is enough to make some think spring has arrived and they will sleepily buzz around. This usually kills them as they use up vital energy which is needed to keep them through the winter.

My House Is Affected By Cluster Flies – What Should I Do?

In most circumstances no insecticidal treatment is needed nor warranted. Unlike most other flies, cluster flies do not carry nor transmit disease. They are at worst a nuisance and this can be kept to a minimum by ensuring that:-

Any water storage tanks in your roof are properly covered to prevent flies accidentally falling in.

Loft hatch/doors to roof spaces are a good fit to prevent flies coming down into the house as they will be attracted to warmth and light (this also applies to ceiling light fittings).

Do not attempt to seal your roof space against the entry of these flies. Your roof space needs good ventilation to prolong the life of its timber and prevent condensation.

Any accumulation of dead or dozy flies are best removed by dust pan and brush or vacuum cleaner.


Smoke Bombs are a highly effective cluster fly killing fumigation device, ideal for flushing out cluster fly infestations from lofts and roof spaces.


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