A cluster fly problem can be very distressing, as all at once thousands of them will turn in either your roof or around your windows.

Learn more about when and why this happens and how I can help resolve your cluster fly problem. 

Cluster Flies – Pollenia rudia

This fly gets its name from its over wintering habit of forming clusters in lofts, window jams etc. The adult is about 6mm long and the body (thorax) is covered in yellow, golden hairs. The adult flies and feeds on pollen and nectar. Cluster flies lay their eggs in decaying leaves and vegetation.  Once the egg has hatched into a maggot, this will seek out worms that are active in decaying vegetation. Once found the maggot will attach itself and bore into the worm, living on its internal organs. As the worm dies the maggot will pupate and emerge as an adult cluster fly.

During the Summer and early Autumn they are no problem for us, but as evening temperatures start to drop in September and October they look to seek out buildings to hibernate in. Large numbers of these flies do produce a sickly smell in loft areas. If lofts are ventured in to during the winter months many thousands may be seen on ceiling joists, roof rafters etc. Water tanks should always be covered to avoid dead flies landing in your tank. During the Autumn/early winter flies will venture down into bathrooms etc via recessed light units, poor fitting loft hatches following tracks of light and heat sources.

Unfortunately flies always come back to the same buildings/lofts and quite often these are lighter in colour! The numbers vary from year to year depending on the temperature. With the correct breeding conditions many generations of eggs may be laid!

Cluster fly problem treatment

An inspection will be required to assess if bats are present in the loft space. It is illegal to use insecticides in lofts where bats could be present. Bats and their environments, for example lofts,  are protected.

Treatment can be by a powered fog generator which propels micro size droplets of insecticide into the loft void accessing all the nooks and crannies. Smoke generators may be used and these also release insecticide into the loft void and kills flies it comes in contact with. This method may be more suitable in smaller loft spaces.


Please call to discuss your cluster fly problem and I will discuss a treatment plan for your property.