Cluster flies are not a problem in summer and early autumn, when they’re still living in fields. We start getting calls in late autumn and early winter when they cluster in large numbers on the sides of buildings, often on sunny windows of houses with light walls.
Before long they will crawl into gaps and crevices in the window frame or roof eaves to find a quiet, dark place to hibernate over winter. This is often a loft, but they’re also commonly found in window frames and even empty rooms.
Although they are not harmful to humans, their presence in groups of hundreds or even thousands is a nuisance and a pest.
Identifying cluster flies
Cluster flies are most common in rural areas. They are slightly larger than the average house fly, dark grey in colour with yellow hairs on their back. They are normally between 6-10mm in length, but there are several different species of cluster fly and it’s not unusual for mixed groups to cluster together.
If you have a large mass of cluster flies on your property, you might notice a bad smell.
What to do if you think you have may have a cluster fly infestation
Cluster flies are not harmful, and move slowly, so if you only have a few flies, they can be dealt with using household fly spray then hoovering them up with a vacuum cleaner. However, it is often the case that there is a large number of flies clustering together (hence the name) so in this situation it is helpful to get a professional pest controller involved.
In this case we would visit to identify the most suitable, safe and effective treatment for your building.
As cluster flies are known to return to the same spot every year, we would also help identify where the flies are entering your property and advise on how to prevent the flies returning next year.