Curiously, it has often been seen that a single house or one building in a row of similar buildings will be chosen year after year for this clustering pest problem phenomenon.
Large numbers of cluster flies hibernating together are capable of producing a sickly smell and, if their local environment becomes warmer for any reason such as central heating in houses and offices, they can emerge to fly around, albeit rather lazily.
For more information about dealing with cluster flies and other insect pest problems contact Prokill who can put you in touch with your local Prokill Pest Control Professional.
Cluster flies (Pollenia rudis) begin looking for protected places to survive the winter in fall.


The presence of cluster flies inside a structure can create health and liability concerns, especially in sensitive locations, such as hospitals, food processing and handling facilities.
Cluster flies usually gain access to interiors through cracks or holes in the exterior walls, or under the eaves of the buildings. Dead bodies of cluster flies inside wall voids, cracks and crevices may trigger allergic reactions in sensitive individuals; in addition they would attract unwelcome pests that feed on them, such as hide beetles, larder beetles, carpet beetles, and carpenter ants. As the weather becomes colder, cluster flies search for more protection from the elements and may be seen in large numbers, particularly in roof spaces, lofts, etc, sometimes with several thousand flies clustered together.

Ants vs termites battle Tiny ants in house plants