Wasps	Rats	Mice	Moles	Cluster Flies	Pigeons

Cluster Flies - Fact File

Size: 6-10mm overall body length.
Markings: Reddish eyes and a thorax covered in golden hairs.
Location: Numerous locations, but usually in lofts and roof spaces. South facing walls often favoured.
Detection: Visual sightings of large numbers of adults.

There are three main species of fly collectively known as cluster flies. They are Musca autumalis, a small fly of about the same size and colour as the house fly, Pollenia rudis, a larger fly dull brown/grey in colour, and lastly Dasyhora caynella which is about house fly size and shiny green/blue in colour.

Biology:

Cluster flies, particularly Pollenia rudis are very common occurring throughout Great Britain. The adult flies after hibernation during the winter months, lay their eggs in the earth or in animal dung. Permanent areas of grassland are favourite sites e.g. permanent grazed pasture or parkland as soil cultivation such as ploughing disrupts the flies breeding cycle. The eggs remain in the earth and hatch when soil temperature increases in the spring. The larval stage is parasitic, entering earthworms and feeding upon them until emerging as an adult fly.

Cluster flies migrate from outdoors into the lofts of houses and farm buildings during the winter months. Obvious signs of an infestation are a roof space containing a large quantity of lethargic flies and a quantity of dead flies. Unless the loft is used for storage purposes or is accessed regularly the flies will hibernate successfully leaving in early spring dependant on the weather.

Reasons for Control:

Cluster flies are not damaging to property when they enter buildings in the autumn purely to hibernate over the cold winter months. As mentioned above they feed on decaying vegetation and earthworms. Cluster flies are not to be associated with dead animal bodies, faeces and the resulting maggots. Fibre glass insulation material in lofts can look unsightly if covered with the bodies of flies that have not hibernated successfully although its insulation properties will not be altered and no damage to the roof structure will occur.

If the loft is home to a hibernating colony of flies, first floor lighting diffusers or sunken spot light lenses can become full of dead or dying flies. This often occurs in houses where the loft area has been converted into a living room. In most buildings built after 1950 the external roof covering has an under felt layer. Cluster flies can successfully hibernate undetected between these two layers. Often cluster flies can be seen basking on sunny grassland or resting on south facing walls of buildings. Cluster flies, like birth return to roof spaces previously occupied so re-infestation is almost inevitable.

Treatment:

If the property is annually infested with cluster flies and a significant nuisance is caused, then the answer might be in late August or early September (before the first flies have migrated into the loft), to place several "Vapona" type fly killers containing an insecticidal wick which slowly emits insecticide into the loft. This creates an unpleasant insecticidal environment for the scout flies that arrive persuading them to possibly choose another more suitable location. If a major infestation is allowed to occur, treatment will be more difficult.

The use of an insecticidal space spray such as a ULV application through a MicroGen will quickly knock down any flies present, but may need repeating several times as flies enter the building at different times.

The use of electric fly control units also work well and can be sold to the householder / property owner. Alternatively they can be rented for the month or so when the flies move indoors.

There is also a theory that previous generations leave behind a scent or pheromone for subsequent generations to follow. The use of a strong disinfectant solution around windows, eaves and soffits etc. is thought to have the effect of removing some or all of this scent, thus rendering the building less attractive to next year's flies.

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