The name cluster flies comes from their habit to clustering together over winter, generally in roof voids/attics, large buildings and churches.
Cluster flies are "field" flies, durning the summer and early autumn they are of no consequence. However, as the weather becomes cooler, cluster flies seek out shelter in nooks and crannies in houses and other buildings.
- As the weather becomes colder, they 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.
- Large numbers of cluster flies hibernating together, are capable of producing a sickly smell and, if their local environment becomes warmer for any reason, they emerge to fly around, albeit rather lazily.
- They are attracted to light, and some will find their way into living areas, and the presence of large flies in winter, usually around windows, can cause concern to the building's occupants.
- They do not present a human health hazard as they do not feed or lay their eggs in waste products
- Cluster flies can be differentiated from house flies by their size, colour and their attraction to light sources
- It is not yet known why they choose a particular place to roost, but once a hibernation area has been chosen, they can return year after year
Controlling Cluster Flies
There is no proven method to prevent cluster flies from choosing their roosting place, but thankfully they can be controlled as soon as they become a nuisance.
At DRE Pest Control we make two recommendations, either:
- By obscuring the roof space, preventing the flies from entering
- Placing an electric fly control unit in the roof space to which the flies are attracted for the winter and place it in the kitchen during the summer.
- Place a ‘fog’ of insecticide into the roof space.