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Cluster fly
 A Pest Controllers guide to Cluster Flies

Introduction to Cluster Fly.



There are a number of different flies that cluster these are

  • Green Cluster Fly Dasyphora cyanella
  • Yellow swarming Fly Thaumatomyia notata
  • The Cluster Fly Pollenia rudis
  • The Autumn Fly

The Cluster Fly Pollenia rudis is the most common and is pictured above and below in someones roof.

Cluster Fly in a Loft
Cluster Fly in a roof space
 Cluster Fly Gathering in a loft


The Cluster Fly

Pollenia rudis 





A large fly up to 10mm in length, very "Furry" in appearance with obvious golden hairs on its thorax (tail end)




The larva (maggot) lives as a parasite of the earthworm Allolobophora chlorotica


The adults lay eggs on the open ground which after about a week hatch.


The newly hatched larva hunt out finds the earthworm and bores into it slowly developing inside it devours the earth worm and eventually pops out of the earthworm and pupates.


As the now young adults emerge  from the pupa they can often be seen sunbathing on south facing walls and fences.


With the onset of Autumn the adults try to enter buildings to over winter and can gather in there thousands in lofts,roofs, upper bedrooms and window casements. When the weather is cold little or no activity can be seen, but on warm sunny winter days they become more active and gather on sunny spots again to sun themselves. In most years there are two generations but when summers are long and warm there can be four. Weather plays a large role in when the flies start to seek out a place to overwinter and again some years it can be as late as December.


The Green Cluster fly in appearance is much like the Green Bottle fly and the Yellow swarming fly is a small fly much like a Gnat. Little is known about either of these flies.


Significance and Economic importance of Cluster Fly


The cluster fly is obviously named because of its habit of forming compact clusters this effects mainly upper rooms which are normally bedrooms and their presence in large numbers can be very disturbing. This is bad enough for private residences but also very bad for business particularly if it is a hotel or any area where guests stay.


The presence of Cluster flies and large numbers of both living and dead flies can also be very off putting for potential house buyers if activity is noted at the time of viewing.


They do not damage buildings except for causing staining in the areas in which they cluster. As the flies do not feed on fecal matter and are not interested in Human food sources they do not present the same health risks as other flies.


In one case we dealt with we were asked to investigate a loft as the client who had just moved into the house  was convinced that the flies were coming from a body which had been wrapped in a carpet which she had seen on opening the loft hatch ! Of course we discovered the carpet was empty and it was Cluster fly after all !


Cluster Fly Treatment


All cases of Cluster fly are different and may need various types of treatment depending on the circumstances, a typical treatment would involve filling the roof void with an insecticide either in a smoke form or as a fog. This will kill the adults which are resident at the time of treatment. There are other factors involved why not give us a call and have a chat about your possible requirements.


Download Information sheet about Cluster fly here



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