Cluster flies can be a nuisance due to the large numbers that can suddenly seem to appear in lofts or around windows during the winter months.
During the summer they live out-of-doors and can often be seen sunning themselves on fences, walls and trees. Indoors, they congregate in roof spaces and dark corners of attics and little-used rooms.
The flies also enter sash window boxes, cracks round window frames and unused Venetian blinds or curtains.
Occasional warm winter days bring the cluster flies out of their hiding places and they crawl or fall into rooms, often covering window sills with buzzing flies spinning round and round in uncoordinated attempts to fly.
In the following spring, the flies start moving again, and the problem recurs. The appearance of these lethargic flies causes considerable annoyance, although they are quite harmless.
Before a treatment we perform a quick survey to rule out any bat activity, water tanks or pilot lights.
After this we would fog affected spaces with a quick knock down insecticide. We can treat any window frames with a long lasting residual insecticide that will remain active for months.
We use a professional fogging machine that disperses a liquid insecticide as a space spray between 15 and 40 microns. At this size droplets are large enough not to be repelled from insects but small enough to remain suspended in the air.
We never use pyrotechnics or “smoke bombs” in peoples homes and we would strongly recommend against purchasing such products.
Next up is an (optional) insecticidal lacquer that is applied to any gaps that may be used for entry. Typically these include opening window frames and loft hatches. This is to try and prevent other types of cluster fly from re-infesting the property later in the season.
Finally, Removal of the dead flies. This is recommended to prevent other pests from moving in and feeding on them. I can return and remove them up for an additional cost. Or the customer can simply vacuum them up a few days later.
Types of common cluster fly
The larvae are parasites of the common earthworm. Eggs are laid in the soil and hatch in about a week. The young larvae bore into worms where they stay throughout the winter. In spring the larvae develop quickly, usually killing the worms, then pupate in the surrounding soil. The adult flies emerge in summer. These are large flies (10 mm long), with a shifting pattern of silver and grey-brown markings on the abdomen, and crinkly yellow hairs on the thorax.
Yellow swarming fly
Is a predacious species, the larvae feeding on aphids living on the roots of grasses. There are two generations a year, the later one usually over wintering as pupae in the soil. However, a warm spell in late autumn may cause the adults to emerge prematurely, and they then invade buildings for shelter when the weather becomes colder. The adult flies are very small (2.5 – 3 mm) and are bright yellow with black markings.
The Autumn fly
Breeds in animal dung in fields. Adult females are almost identical in appearance to common house flies, but males are distinctive in having an orange abdomen with a black mark down the centre