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How To Control Cluster Flies

The Problem with Cluster Flies

Cluster flies can be very distressing when they turn up in the autumn and sometimes in the spring too. They come in thousands and suddenly appear either in your roof or around windows in the house.

There are two main species that cause concern but many others exist.

The house fly sized Pollenia rudis and the fruit fly sized, Thaumatomyia notata. These flies can also be described as "swarming flies" and "small yellow swarming flies".

These flies breed throughout the summer in the fields, sometimes using earthworms to support their larvae by laying eggs into the soil and the resultant larvae seek out worms in which to subsequently complete their life cycle as parasitic larvae.

When searching for cover for winter hibernation, these flies will gather together mainly on south and west facing elevations of structures and in late autum afternoons may rest on these walls in the sunshine but venture up into the roof space, loft or in and around window frames in the evening where they stay overnight. As winter comes, the cluster flies stay within the roof void and only then venture out on early spring sunny days where they may sun themselves on the roof tiles. Sometimes they stay between the roofing felt and the tiles, which makes treatment a little more complicated.

Dead cluster flies on the loft floor can lead to infestations of undesirable insects such as carpet beetle, which may subsequently invade the house and feed on fabrics. It is adviseable to clear up dead flies where practical.

Cluster Flies can also be a problem behind wall cladding whether it be a timber clad wall or a tile hung elevation. These flies can enter through the very tiniest of holes and you may think your cladding is close fitting and not susceptible but sadly, these flies can probably gain access. To deal with this issue you will need to blow an insecticidal dust up behind the cladding. This can be fairly easilly achieved with the use of a pressure duster. Search the Bellows Duster or DR5 Duster from the search box on the top right of each page on the site. You will need to use Insectrol Powder 150g to kill the flies, again, use the search box to find this product. You may prefer to call us for more advice for this particular application.

Controlling Cluster Flies

Before treatment, we suggest you check if there is any evidence of Bats. If there is evidence of Bats then insecticides MUST not be used.

Generally, treatment in the roof void will significantly reduce the problem, however, expect a new lot of flies the following year as it is thought they leave a pheromone in the roof which is attractive to next years clutch of cluster flies / autumn flies / roof flies.

Three main methods can be utilised in the roof void:

1. Installation of an automatic aerosol dispenser (battery driven) with cluster fly killer aerosol. Click here to go to the product.

The automatic aerosol dispenser dispenses Prevent Auto on a set programme which can be adjusted to suit the size of the roof or the extent of the fly infestation. The dispensers are battery operated.

2. Installation of an electric flykiller specifically designed for cluster fly use.

Electric ultra violet light fly killers are ideal for control of cluster flies as they collect the flies in a specially built fly catch tray that is designed to contain many thousands of flies and prevents the catch building up to disrupt the safe operation of the machine.


3. Periodic application of Power Foggers or Pro-Active Midi Bombs for one off quick kills of flies.

Power foggers and smoke bombs can be very effective but may need to be used more than once per season. As the flies enter the roof over a period of weeks, your first treatment may eradicate all the flies in the roof but within days, more cluster flies may arrive. If you discover the fly problem let''s say, in December, then a single treatment in this way will clear the problem until at least March. you may then have new flies entering for about two months.

For controlling cluster flies within the home there are a range of products, including window cluster fly traps, sprays, smokes etc. Cluster flies commonly gain access around window frames on south and west elevations of properties. Click here to go to the products.