Cluster Fly (Vespula vulgaris)
Cluster flies are parasites that live of earthworms. The eggs are deposited individually into cracks in the soil of lawns and open areas in late summer or early autumn.
The eggs hatch in approximately three to seven days and the larvae then enter the body cavities of earthworms to overwinter until spring when feeding activity resumes. The larvae feed for up to 19 days on the eathworm, then moult and begin the final larval stage. The larvae finish feeding on what is left of the earthworm host and then move into the soil where they pupate for approximately 10 weeks. In mid-summer, the adults emerge from the soil. These adults and the cluster flies that hibernated in households will mate and lay eggs in late summer or fall, repeating the cycle. Adult cluster flies can often be seen sunning themselves on stumps of trees and sides of houses in autumn before they hibernate.
Cluster flies, particularly the Pollenia rudis are very common occurring throughout Great Britain. The adult flies after hibernation then lays eggs in the earth or animal dung. Permenant areas of grassland are favorite sites, such as permenantly grazed pasture or parkland as cultivation thru ploughing disrupts the flies breeding cycle. The eggs remain in the earth and hatch when soil temperature rises 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 is 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 do not cause damage to property, they enter buildings in the autumn to hibernate over the cold winter months. They feed on decaying vegetation and earthworms. Cluster flies are not 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 birds, return to roof spaces previously occupied so re-infestation is almost inevitable.
Whilst there is a specific species of common cluster fly (Pollenia rudis), there are other species of cluster fly and swarming flies which have a similar hibernating nature and these may also be involved in forming mixed populations of flies inside suitable buildings.
The life cycle of the Cluster Fly is very much dependent on the prevailing weather conditions, and in this country, two generations a year are usual but in hot summers, up to four generations per year are possible.
Cluster flies are “field” flies and in summer and early autumn they are of no consequence. However, as the weather becomes cooler, they seek out shelter in nooks and crannies in houses and other buildings. As the weather becomes colder, they search for more protection from the elements and may be seen in large numbers, particularly in roof spaces, lofts, etc, sometimes with several thousand flies clustered together.
A single house or building in a row of similar buildings will be chosen year after year for this clustering phenomenon. Large numbers of cluster flies hibernating together are capable of producing a sickly smell and, if their local environment becomes warmer for any reason, they can emerge to fly around, albeit rather lazily.
They are attracted to light, and some will find their way into living areas. The presence of large flies in winter, usually around windows, can cause concern to the building’s occupants. However, whilst cluster flies can be a source of nuisance on occasion, it is not considered that they pose any risk to human health and their presence should not be taken as evidence of poor hygiene.
TREATMENT
A fog treatment of the roof space either with a specialist ULV machine or smoke generator will alleviate the problem, call us now to arrange a treatment.
Notes
Will see an influx of cluster flies on cold nights.
Cluster flies are generally trying to squeeze into gap between the window and the frame.
They will also find their way down from the attic after being disturbed by light, heat or vibration
Internal treatment
Mainly upstairs bedrooms and bathroom, particularly south facing bedrooms, and rooms with recess lighting going up into attic.
Cluster buster
cluster busters are placed at bottom of window on the glass pane – they will collect a large majority of flies, rather than having them pile up dead on window sill or floor
twin pane windows – 1 x unit
large sache windows – 2 per unit
patio door – 2 per unit
Spray insecticide directly on fly – will kill it within 30 minutes, will be lying dead somewhere
Residual insecticide on window sills, frames, reveals, – will be dead on sill or window
Sunburst natural fly killer – is an Ultra Violet sticky board trap which is very effective, must be turned on
Available in Black, White, Silver grey, Bamboo (out of stock until November 215
Ultra violet electrical fly killers may be an option – but also present a fire risk
External treatments
Can at a push use insecticide on walls – will break down or wash off
Best recommendation;
Treat loft if no bats
Treat windows internally
Install cluster busters and sunbursts
Try to put package price together to include everything as one price – problem is customer’s expectations