What do they look like?

Cluster flies are a relatively large insect, about 10mm in length with a wingspan of up to 20mm. Under a microscope it will be seen that they have golden hairs on the thorax (upper part of the body) and the abdomen has a checkered pattern.

• They are found in late autumn and through the winter in the roof space of buildings. It may be noticed that several flies are evident each day in upstairs rooms. That is because the cluster flies have moved into the roof space for protection for the winter period. Some of them will have been attracted to the light shining through the ceiling rose in any of the upstairs rooms and have found their way down through the light fitting into the room.

• An examination of the roof space may reveal very large numbers of these flies as they cluster together to conserve energy (hence the name cluster fly)

• They are not regarded as harmful and are not known as vector of diseases but can be regarded as a considerable nuisance due to their numbers.

• They do not breed in the winter nor do they feed, so their numbers will not increase through this time.

• If left undisturbed they will remain in the roof space until next spring or early summer when they will return to the fields to breed.

• Unfortunately it has been found that once they choose a location they will return year on year because it seems they leave a pheromone behind to attract them again at the end of the season.

• It is almost impossible to proof the roof to prevent access and therefore the problem will continue.

• There may be a period when the flies are entering the property for the night but still going outside during the day. This creates a problem in trying to treat them in the daytime, as the flies will not be there. Because of this it is sensible to wait until the weather turns much cooler and the flies have moved in permanently before a treatment is done.

How can the Council Help?

• Highly trained officers from the Pest Control section can undertake a treatment for you; there is a charge for this service (See the web link for prices).

• The officer will undertake to treat the roof space with a low volume insecticidal mist, this will kill most of the infestation but some may detect the insecticide very quickly and may exit the roofs pace before being overcome.

• He will advise you of what he has done and what the likely outcome will be he will leave you a safety sheet providing information about the insecticide that he has used.