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.
The Cluster flies will hibernate in a number of areas; the reveal of windows, under roof tiles, openly in the attic, between roof membranes, voids behind plasterboard of walls and ceiling etc., each of these areas will offer different levels of protection against cold.
There will also be a number of different changes to the environment that may trigger flies to move either into or away from a property; temperature variance (as the temperature drops they will enter a property, as temperature rises they will attempt to leave a property), the ambient light level given off from a house or a particular location,, ambient temperatures in a property and in the external environment, open windows, gaps in window frames, tiles, soffits etc. Flies under tiles might emerge on a sunny day to absorb some sunlight, before returning to their hidden location, but because lights are on some maybe attracted into the living area instead. Often cluster flies come down from the roof space because a halogen down-lighter has been turned on, the heat from the bulb triggers them to come out of hibernation and the light attracts them downwards into a living space.
Each cluster fly infestation needs to be looked at on an individual, unfortunately there is no magic bullet for completely eliminating cluster fly infestations. However there are a range of options that can be utilised to manage the problem and reduce its impact upon you and your surroundings.
Roof spaces and attics/lofts
Ultra Low Volume (ULV):
If the main problem is occurring in the roof then 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. Dependent upon the quantity of flies it may be wise to arrange for either ourselves or someone else to lay some plastic sheeting beneath the flies wherever possible to assist in cleaning up the bodies. This is a knock down treatment that has a very low residual effect. There are options available for surface spraying with an insecticide that has a longer residual, but these are very much dependent upon the scenario and require a proper inspection.
Ultra Violet Electic Fly Killer:
If you are finding that you need to carry out this treatment repeatedly thru the cluster fly season, October to April, investing into an Ultra Violet EFK may be a better solution, these need to be checked on regularly to ensure there is no risk of fire created.
We have recently added the the cluster buster to our range of available solutions to assist in controlling the build-up of dead cluster flies in the living area around the windows. The cluster buster is a fall trap that can be attached to any window pane. Hidden inside the cluster buster is a thick blanket of patented, non-toxic odour suppressing QuickSand™ (a powder made from exploded egg shells). The flies are attracted to the light radiating through the windows, when they hit the glass they fall directly into the Cluster Buster where the powder clings to their feet and hairs, preventing escape. Once trapped and out of sight, the struggling flies sink deeper into the powder as though trapped in quicksand, piling the insects layer upon layer!
The Cluster Buster has no sticky liners or foul smelling liquids to replace, no chemicals to harm our environment, and works silently until its chamber is full.
Each Cluster Buster trap can hold up to 1000 cluster flies!
Prices range between £17.49 and £19.49 per unit, inclusive of any taxes
This has an elegant and decorative design that conceals a glue board that catches the cluster flies. It’s discreet, stylish and environmentally responsible, fitted with a powerful 20 watt compact ultra violet tube and can be used wall mounted or free standing. It takes advantage of the fact that the cluster flies are attracted to UV light. It can be placed any where in a room and has an effective coverage of 35sq m, therefore closer to the point of access the better. The light is non harmful utilising UVA light (UVB is the light that causes sunburn and skin cancer). Bulbs (shatter-proof available) do need to be changed annually to remain effective, and sticky pads need to be changed when no longer effective.
Prices range between £56.95 and £62.49 per unit, inclusive of any taxes
Residual Insecticide internally:
We can apply a residual insecticide to the window sills and the reveals.
Residual Insecticide externally:
Generally speaking an application of insecticide is not going to be beneficial, as the weather reduces an insecticides active residual effect. However on occasion we do come across a property (generally larger country mansions) that an application can offer benefit from the use of an exterior insecticide treatment. Best discussed during an inspection.