We have received an email asking for advice from someone who has been troubled by an influx of flies inhabiting their window frames and attic.
This is not an unusual occurrence in some properties. It appears to be totally random as to which properties appear to attract them. These common flies and cluster flies are only searching for a home for the winter. In order for this to happen, the flies need access to an area of refuge.
The flies are attracted to fairly consistent temperatures and prefer to be kept above freezing point. Bearing in mind the recent cold snap, it is not surprising that every fly determined to make it through the winter has sought refuge. This is an occurrence in any autumn month and perhaps worse this winter than for a number of years.
Older roof spaces generally provide easy access due to a period roof covering not having a second impermeable membrane, but a newer roof covering which is appropriately covered should have ventilation in place. This ventilation provides access for the critters.
Rock wool and other fibre roof insulation material not only helps keep the living accommodation warm, it also provides an insulated home for any flies that wish to live at a lower level rather than nestling out of the drafts between the common rafters and the underlay.
Prevention is better than cure if this is a regular problem. If you have to address this problem, making the environment less attractive for the invaders is often the best approach. This can be carried out by a spray attack with an insecticide or fly spray in the attic to provide an unpleasant environment with especial regard to around the openings where entry into the roof space is possible.
If you have to venture into the roof space and swarms are already in residence, an attack with the fly spray is almost your only choice. However, this can leave copious quantities of dead flies covering everything in the roof space that will require hoovering or sweeping up (often very difficult), and this could also contaminate the water supply.
Caution should be taken if there are any bats in the roof space. The bats will of course eat some of the flies but they are also a protected species under the Wildlife and Countryside Act 1981 (as amended) and the use of insecticides may therefore constitute an illegal act.
Prevention can also be carried out in a greener and more pleasant way by spreading sprigs of strong smelling plants in the attic space, such as basil, mint, garlic, lavender and rosemary and other similar strong smelling herb plants. These sprigs will regularly require replacement as the odour fades.
Around windows similar principles apply. Plants can be planted outside or strategically placed inside on window cills to reduce ingress. Modern windows such as those set in UPVC window frames or those factory or mass produced in softwood frames with air vents and trickle vents are most susceptible. These leave pockets of warm air where the flies like to take up residence in their efforts to survive.
Wiping the window joints clean with warm soapy water on a warm day (so the joints can then dry off) should be carried out. Immediately after the windows frames are dry, the surrounds can be sprayed with a fly spray, the odour for which lingers long enough to create fly free windows until the following Autumn.
5th January 2011
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