Cluster flies can be difficult to remove, but it is possible with some effort. First, try to identify where the flies are coming from, such as cracks or holes in walls or windows, and seal them up. Then, you can use an insecticide aerosol spray to kill any remaining flies. Vacuuming the area can also be effective, but make sure to dispose of the bag afterwards to prevent the flies from re–infesting the area. You can also hang fly traps in the area to attract and capture any remaining flies.
What are cluster flies
Cluster flies look very much like house flies but are bigger and greyer. They have black-and-yellow striped legs and a yellow abdomen with two clear wings. They gather in large numbers during late summer and early autumn whilst seeking sheltered places to hibernate during the winter.
Cluster flies are a summer pest that is most noticeable when it emerges mid-spring to begin mating. Cluster fly larvae feed on the decaying organic matter in the soil, leaving behind black, tarry fecal deposits and tunnels through the top layer of soil.
Adults: cluster flies emerge from hibernation about a week to 10 days after snow melts. Adult cluster flies often appear in the windows or doors at night as they return to their hibernacula (hibernation sites). They can be identified by their small size (3/8 inch long), color – dark grey or brown with a slightly yellowish sheen, hairy thorax and clear wings with smoky tips. Its mouthparts look like a pair of wire cutters and are used to shear through the skin of earthworms.
Adults live harmlessly out of doors in summer but may enter buildings (usually rook smaces and lofts but also through windows into rooms) in autumn to hibernate, sometimes in vast numbers.
Eggs laid in damp oil, rotting vegetation. HAtch in about a week. Larvae soon after emergence seek out and parasitise earthworms, which are eventually killed. Adults are 6mm long, blackish, with fine golden hairs and thorax. Often 2 generations per year.
There are over 20 species of cluster fly in the UK; Pollenia rudis is the most common.
Cluster Flies Distribution And Habitat
Found commonly throughout Europe and the UK. The common name refers to its habit of clustering and hibernating in numbers of buildings.
The life cycle is very dependent on weather conditions. In Britain it seems that two generations per year are common and in hot summers up to four generations per year might be possible.
The adult flies, replemendent with their thorax clothed in golden hars ( which often rub off), feed on the nectar of garden and wild flowers.
When do cluster flies become a nuisance
During the summer and early autumn these flies are of no consequence. As the season cools they seek shelter in nooks and crannies in houses and other buildings. As temperature drops they search for more protection and frequently form vast clustering masses in roof spaces and lofts. It has often been observed that the same house or building in a row of similar buildings will be chosen year after year.
Such large aggregation of flies do produce a rather sickly smell and, if warmed-up accidently or artificiently during their hibernation, may emerge rather laily and create some consternation among people using the building. This has occurred commonly in church halls, domestic bedrooms and has ever been recorded as a problem for fly- contaminated switch-gear in heated automatic telephone exchanges.
Cluster flies become a nuisance when they enter a building during the autumn to hibernate or when they start to emerge in spring or occasionally on warm winter days. You may want to get rid of cluster flies even though they aren’t a health hazard in the same way that house flies are. They only enter a building to hibernate, not to breed or feed.
How do I know if I have a problem with cluster flies
If you have a cluster fly problem or infestation you will notice dead, dying or lazy live flies around windows or in roof spaces. You may even see them sunning themselves on outside walls. You will only see them on warm winter days, in the spring and early autumn. Flies in the summer are likely to be house flies, bluebottles or other types of flies.
Cluster flies are generally most common in a rural environment. Heavily infested buildings may contain several thousand flies which can be a serious problem.
Cluster Fly Control And Extermination
Autumn fly ( or face fly) (Musca autumnalis)
Autumn fly is the common name for “Musca autumnalis “, a species of fly in the family of Muscidae. It belongs to the subfamily, “Pseudo Muscinae”. A fly very similar to the house fly in appearance but distinguishable by its clearly defined striped grey and yellow abdomen and by the eyes of the male witch almost touching along the center of the head.
The female autumn fly lays its stalked eggs on animal dung in fields and larvae develop within the dong and pupate in the surrounding soil. The adult flies tend to feed on body secretions of stock in the fields and have been recorded drinking blood, although they are incapable of piercing animal or human skin. Their hibernating behavior is very similar to cluster fly and they frequently form mixed populations inside suitable buildings.
Green cluster fly ( Dasyphora cyanella)
In the same family (Calliphoridae) as the quite common greenbottle Lucilla and very similar in appearance, Dasyphora can usually be distinguished by its fairly distinct, two longitudinal dark stripes on the thorax.
This is another species where the larvae develop within the dung on which the adult female has laid eggs. As with all outdoor insects, the life cycle is very dependent on weather conditions: from egg to adult may take anything from six to 10 weeks, and the adults are usually active from early summer right through to the onset of cold late autumn weather. The seeking of hibernation sites is similar to the preceding species and the green cluster fly is frequently a member of mixed swarms in roof spaces.
Yellow swarming fly ( Thaumatomyia notata )
This is a much smaller species of hibernating fly, seldom being longer than 3mm, with a typical chloropidae fly appearance – daily large rounded wings in relation to its small yellowish rounded body with black markings, It may be confused with fruit flies.
Yellow swarming fly ( Thaumatomyia notata ) isa native species that has been observed in the wild since at least 2002. It is apparently attracted to lights, which means it’s a nocturnal flyer, unlike most other swarming flies that are diurnal. This could be one reason why this fly hasn’t been documented with great frequency since its initial discovery.
The window fly ( Anisopus fenestralis )
The adult fly is about 3-4mm in length, reminiscent of a small crane fly, with noticeable long spindle legs and fairly prominent antennae. The wings, with a fairly complex venation, may sometimes be seen to have cloudy grey/brown patterns. This is one of several species of flies commonly found to infest sewage works, sometimes in very large numbers and producing giant swarms. It is one of the most common species to enter houses and other buildings, frequently seen on windows, lodges and frames. The adults will attempt to hibernate with the onset of colder autumn/winter weather but only a small proportion of these will survive the winter. Of greater significance is a common habit of the female fo tly to lay eggs in any dump situation, often resulting in foodstuffs in the domestic pantry becoming infested.
Control Cluster Flies
Control methods for the above cluster and swarming flies have been little researched and they are often ineffective or, at best, incomplete. It is often not possible to prevent flies from entering premises or to persuade affected householders that the flies, while a great nuisance on occasion, are unlikely to represent a health risk, do not breed indoors and are not indicative of poor hygiene.
Control of the flies outdoors in their breeding areas is considered impractical. In recommending a combination of physical and chemical control methods, it is recognised that proofing against fly entry is seldom 100% effective. Caulking around window frames and sealing other entry points can contribute greatly to control. It is difficult to use insecticide in and around “unsealable” entry points to some buildings, e.g. thatched roofs or under tiles or slates, but in some situations where recurrent problems have been experienced, prophylactic dusting of likely access points can be partly effective.
Once the flies are inside, e.g. in a loft or attic, control is relatively simple with both physical methods and a range of insecticides and formulations. Occasionally a vacuum cleaner (nozzle type) can be used as the sole control method where aggregations exist within reach and the collected flies can be disposed of in a sealed bag, e.g. in the vacuum bag inside a polythene bag or similar. Alternatively, or in addition, most pyrethrins/pyrethroid based space sprays wili quickly kill exposed flies and in some situations smoke formulations based on permethrin can be very effective. Special care must be taken to follow label instructions, particularly in view of the fire risk
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