Treating Cluster Flies in the Home Or Workplace

CLUSTER FLY (POLLENIA RUDIS)

The Cluster Fly is named so due to its habit of clustering and hibernating in large numbers in buildings and loft spaces. This fly is commonly found throughout Europe and the UK. These flies are not classed as a pest species, but often require treatment due to their large numbers. During the summer and early autumn these flies are of no consequence. As the season cools they seek shelter in nooks and crannies in houses and other buildings. As temperatures drop they search for more protection and frequently form vast clustering masses in roof spaces and lofts, with several thousand flies clustered together. It has been observed that a single house or building in a row of similar buildings will be chosen year after year for this clustering phenomenon. Such large numbers of these flies can produce a sickly smell. If warmed up either accidentally or artificially they may emerge from hibernation and become a nuisance to the people using the building.

The adult cluster fly is a fairly large species at around 10mm in length and a wingspan of around 20mm; it has large reddish compound eyes. the thorax (body) has a distinctive dark greyish/ olive colour and is covered in golden hairs. When resting the wings are held tight on top of the abdomen.

The adult female lays her eggs loosely on and around damp soil, beneath dead and rotting leaves etc. after about a week the larvae hatch from the eggs and actively seek earthworms to which they cling and bore through the body wall. The conventionally shaped fly maggots develop within the earthworm. The larvae have been observed to push their hind ends back through the earthworm's body wall to allow their breathing spiracles to gain access to free air. At or near to the end of the earthworms life the larva will bore its way out and pupates in the soil. Since this is a free-living field insect, the life cycle is very dependent on weather conditions. In Britain it seems that two generations per year are common, but in hot summers up to four generations are possible.

There are various different ways of treating for cluster flies. The easiest way to deal with them is to use mini smoke generators and this will kill the nest off. An installation of an automatic dispensing insecticide system would be beneficial to stop further infestation occurring. When using smoke bombs or smoke generators to control cluster flies remember to make sure that bats are not present and water tanks are fully covered.

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