Cluster Flies

The Cluster Fly is often mistaken for the common house fly but they are more sluggish and often appear to fly very slowly. They can overwinter in vast numbers in lofts, cellars and dark voids. These flies are of no particular harm but can be alarming because of their great numbers. Generally noticed on the first warm days of spring when they congregate on the inside of windows. Frequently found in window frames, particularly sash windows. Interesting life cycle - lay eggs in damp earth and resulting larvae migrate into the bodies of earthworms where they develop into maggots which then bore out of the worm to pupate. Easily controlled with spray, fumer or electronic device.

Your Questions Answered

Q.
Hi Rowland, I have a SWAK dispenser in my loft to control cluster flies, which I have found works very well. My question is, when should the dispenser be active, and when can I leave it switched off? Thank you, Michael (Swindon).

Hi Michael,

I would keep your ammo dry for as long as possible, the refills are quite expensive. The flies will not be active during this cold weather so no point in having it in use right now. Come the warmer days of Feb/March/April it would be worth re-activating for short spells. Choose still, calm days so the insecticide does not get sucked or blown out before it has time to work. The real time to use it is Autumn when the flies come into the buildings to hibernate. Hopefully by now anything in the house is long since dead.

Q.
Hi. I have a cluster fly problem at my cottage in France (which is a holiday home). They appear in late September onwards, and congregate at windows trying to get out. They leave deposits/spots on my curtains - is there a spray that I can use on my curtains so that the flies avoid them (they leave spots on my windows too but at least I can simply wipe them clean). Thank you, Nicola

Hi Nicola,

This is a very common problem. If you are infrequently at the house then perhaps the best remedy is to install a SWAK insecticide dispenser (available on our website) either in the house or preferably in the loft space where the flies will initially congregate. That unit will dispense a measured amount of insecticide at intervals you can select and will kill the flies before numbers can escalate. (Not to be used if bats or bees are resident in your loft)

Q.
Hi Rowland,I have a house in France which has been empty over winter I've return to find the loft infested with tiny flies all stuck to the walls they are only 2 to 3 mm in size any idea what they do they pose any threat to building structure ? and how to cure them Thankyou Ian Creuse

Hi Ian,
Very sorry, French flies are outside my ken. I doubt they will be a threat in any way but the simplest way to eliminate them is with an insecticidal smoke bomb or two, depending on the loft volume. Make sure you have no bats before using the smokers.

Q.
The last few days have been unusually warm and I have large numbers of cluster flies at the sash windows in South facing rooms at the moment (inside and out). Are these flies on the way into the house looking to hibernate or do you think they were already in the house (e.g.in attic or window sash boxes) and the unusually warm weather has revived them? Is there a product for application to external walls and around window frames etc to reduce the number of flies getting in? And finally - is there an attic "bomb" treatment which is safe for bats? Andrew

Andrew
A fumed is by far the best way of getting a quick knock down effect. This cannot be used where the bats are I'm afraid as they are a non target species and protected. It could however be used in the room where the cluster flies are gathering as it leaves no lasting effects, such as smoke residue. Protector C is an effective insecticidal spray safe for use in the home. This can be used as a space spray and also onto hard and porous surfaces. We sell a kit for cluster flies called Blitz Kits for cluster fly. It contains the above two products plus an Agrothrin powder which can be applied in any cracks or crevices where the insects may be entering.
Good luck

DIY Pest Control
Customer Service

Sent from my iPad

On 29 Sep 2011, at 23:01, sales@diy-pest-control.co.uk wrote:

A user has submitted the following question:

The last few days have been unusually warm and I have large numbers of cluster flies at the sash windows in South facing rooms at the moment (inside and out). Are these flies on the way into the house looking to hibernate or do you think they were already in the house (e.g.in attic or window sash boxes) and the unusually warm weather has revived them? Is there a product for application to external walls and around window frames etc to reduce the number of flies getting in? And finally - is there an attic \\\"bomb\\\" treatment which is safe for bats? Andrew

Q.
We've recently moved into the top floor of an old manor house converted into apartments - set in mature gardens of 6 acres with many surrounding trees. In the summer we had major problems with honey bees - then wax moths and now the latest is lady birds and cluster flies there are 19 single glazed sash windows in the apartment and I am currently having to collect about fifty flies each day from the windows - one month ago it was up to 200 a day! There is a very large attic but can't see much evidence of them there - I'm beginning to wonder about fitting secondary double glazing on some of the windows on the south end of the building where most of the infestation occurs - but this would be very expensive as it's a listed building. Any suggestions would be much appreciated. Management is responsible for coping with the infestation but they don't seem to know what to do other than pay for the occasional visit by a pest controller. Peter

The solution we usually recommend for cluster flies is the Blitz Kit for Cluster Flies because it contains everything you need. One Blitz Kit will be enough to treat a room up to 400m cubed. Evacuate the room closing all the windows and doors and making sure any pets are removed or fish tanks covered. Light the fumer and leave for a couple of hours after which time you should open the doors and some windows to clear any residual smoke. There will be no smoke or residue left. Treat all surfaces and soft furnishings with the spray and fill any cracks and crevices where the insects might be entering with the powder. although you say there is nothing in the loft it might be as well to treat there as well as this is normally the source for cluster flies. Another solution for the loft would be a swak dispenser which dispenses at intervals which you determine over a period of time. Each refill lasts about 30-60 days depending on the frequency

Q.
When can I stop using smoke fumigators(to kill cluster flies) in my loft?

Cluster flies are a problem in loft spaces in the spring and autumn. I would suggest that as winter sets in fumigation is no longer necessary, but be vigilant as spring returns in case the cluster flies do too!!

Q.
The last few days we have had 6-7 flies appear in the house, they are big, black and slow moving. we can not locate where they are coming from, do you have any idea's where we should start looking?

It's very difficult to say. I would suggest they are being attracted by something rotting. Check under floorboards, behind cupboards etc in case any rodents or small animal has found its end there. Other than that I assume you have looked in all the obvious places.