A Plague of Flies

BnB

I'm not sure if this is the best forum for this. Mods - feel free to move if you think there is a more suitable one.

We are suffering from nothing short of a plague for flies at the minute. The problem is up stairs in our house. The house is a 1 and a half storiy with 8 velux windows upstairs.

The Velux's seem to be a particular hiding spot for them. Every Saturday I go upstairs with the hoover and open the velux's and clean them out. When I open them, the best part of a hundred flies, most of them dead, will fall out from around the frame of each one. I clean them up and leave the windows open for the day and they will be mostly cleared. But as soon as I close them again, they will start building up again.

The house is span new. we're only moved in a few months.

We don't really use upstairs at all except for my office (I'm sitting here with 3 or 4 of the backstards buzzing around me right now). But all the rooms up here are finished/carpeted etc.

Talking to two friends at the weekend and they are having similar problems. In both cases, the houses are fairly new and in both cases it is around the Velus windows they really have the problem.

Has anyone had a similar problem and managed to solve it.

Rockery Woman

I live in a one and a half storey house with velux windows and I have exactly the same problem!!!

Every morning I open my 3 velux windows and I am besieged by bluebottle flies - they get into the ventilator part to hibernate for the winter.

I just quickly open the window, dose them with a shot of flyspray and they fly away to die elsewhere.

My house is 4 years old but this is an on-going problem. I can hear them buzzing sometimes trying to get in through the ventilator (under the handle of the velux) - horrible little dirty b******s!

When the colder weather arrives the flies will disappear though, but at least if you open the windows even for a few minutes every day you will get rid of most of them.

damagegt

I worked converting attics for years and have seen this many times.There called cluster flies.There more then likely nesting in attic/storage spaces up stairs.They hatch late summer and are not the easiest thing to treat due to the fact of where they nest.

burly

Bear in mind, the unusually mild weather in the last few days has seen a dramatic increase in the number of flies around. We swept up 100-200 flies from our office lobby window yesterday, including wasps. And i hadnt seen a wasp for 3 weeks before then.
As said above, the cold weather will sort them out.

BullBauld

I have the same problem in my new build. It's a 2 storey and there are a hape of them in the attic. Could hear them bouncing off the felt one day(attic not insulated yet). Couldn't believe how many there was and as damagegt says they were gathered in clusters.

I went up and dosed them with a can of fly spray, did the trick but the hoors were back in full force a few days later.

So Rockery Woman you reckon they should be gone with the cold weather? Good cos I'm moving in in a few weeks and want rid of them.

Mike2006

Same problem here in attic.. Have sprayed them a few times but more seem to come back.

Any way of getting rid of them for good or will they come back every year??

Mike.

galah

same problem here - they seem to sit around the edges of the velux windows (where the bottom part of the window closes against the wall, and up on top underneath the handle for the window). It only affects the velux though - we have 'normal' windows on the sides of the house, and no flies there.

Could it be an installation/design problem?
Only seen it here in ireland though, lived in lots of houses with velux windows on the continent and never had that problem before.

damagegt

As i said above there cluster flies.if you do a google it will tell you all about them.The problem about leaving them until the cold is they lay dormant until next year so it doesn't treat the problem and they will more then likely return the following year.

BullBauld

So whats the best way to treat them damagegt?

Find where they are nesting/hatching and destroy that?

r3nu4l

Wow, I've had this problem on and off for a couple of years. Never knew they were cluster flies. Thanks gadgetgt!

Just found this

The velux windows aren't the problem (before we see stories pervading the internet that Velux causes fly problems ). I've no Velux windows but four years ago when we bought our house I kept noticing flies in the landing and dead flies would fall out of the loft when I opened the hatch. I thought that a small animal had died in the attic but could never find anything (or the flies either!!).

Early this year we had a real problem in the kitchen when I was killing up to 100 flies a day That went on for weeks upon weeks and eventually I found the source (at the back of the cupboard behind the sink). They eventually went away.

Glad to see I'm not the only one suffering For the record, my house was built in the 1930's and is a 3-bed Semi, so it's not confined to new builds Also, I live in the UK and the council leaflet above (not from my local council) seems to indicate it's a UK-wide problem.

I also just found this

Seems as though they are common where there's plenty of earthworms and lush grass. I imagine that sites of new builds will have lots of earthworms by virtue of the fact that the soil gets churned up a lot during the build process.

Advice from Portsmouth city council here

Wiki
ArticlesBase

Rockery Woman

So Rockery Woman you reckon they should be gone with the cold weather? Good cos I'm moving in in a few weeks and want rid of them.[/QUOTE]

Yeah - a good sharp frost should get rid of them. Good luck in your new house.

j timber

hi guys i`ve exactly the same prob in our new build..thought it was the insulation as we got it blown into the attic...there are loads up there buzzin round. as we have no hatch dr they all coming down into rm below. so if the frost kills them off what happens nxt yr??same prob again?

Rockery Woman

yep J Timber - afraid they are an annual event, in my house anyway! Open the windows every day, whoosh them away, next day - theyre back!

Opened mine this morning, there were a few there but not as many as last week before the weather got cooler. Im hoping in another week theyll be scarcer.

FriarTuck75

Went up to my attic last night and we have hundreds of them in between the rafters up top. They look like those cluster flies that others mentioned. A sickening sight, we had dead ones 2 years back when we moved in and I just presumed these were from when the house was being built. I hate the little feckers with a passion. Is it worth going up with a hoover and sucking them up or is this just a waste of time to this now? Better wait until the cold weather arrives and they die off?

Is it a waste of money getting Rentokil in to treat the problem now with the cold weather on its way? Do these guys look for access points and treat these areas as well?

BnB

Thanks for all the replies. As Rockery Woman said, the cold weather seems to be doing a job on the alright. On my extermination run yesterday morning, numbers were well down. It sounds like it is just something we are going to have to live with ...!!!

dh0661

The guy in my local fruit & veg has a little knacky thing to trap the small little fruit flies.

He reckoned if he put these little traps in a freezer for a few days they would die, you would imagine they would.

He told me lately that he took some of his trap thingies from the freezer but forgot to dump them, the next day when he looked at them he noticed that the "little &astards" had come back to life, they looked dead when they were frozen.

The only conclusion can be that the cold/frozen weather only lays them dormant and will not kill them off.

Maybe same story for larger type flies. :eek:

damagegt

Hay all.I see this problem has grown since i was last here.To be honest I have no idea how to treat them as i have never had them only met them numerous times while working.But Im sure a goggle or a call to a local pest control will give you more insight.Anyway glad i could help.;)

Mike2006

Right,

Having found this thread, I looked into it a bit more and explored the options:

1. Purcahse items online and deal with it myself
or
2. Get in the exterminators

1. This is the one I went for. Basically I purchased a couple of foggers online that I will release into the attic. That will kill off the current population and then I purchased another 'automatic' spray and dispenser which 'should' keep them out. A can of spray will last for 3 months in the dispenser so i will see how it gets on.
You can also get another solution which you mix with water and spray on the walls of the house which will stop them from landing on it.
Cost was about €100 inc delivery for all the stuff.

2. Rang a well known national extermination company and the cost was €350 for a cluster fly extermination. This included first visit and a 2nd visit a month later. It was just a kill though, not a preventative measure so I decided against it.

Mike.

whitelightrider

Mike2006 wrote: »

Right,

Having found this thread, I looked into it a bit more and explored the options:

1. Purcahse items online and deal with it myself
or
2. Get in the exterminators

1. This is the one I went for. Basically I purchased a couple of foggers online that I will release into the attic. That will kill off the current population and then I purchased another 'automatic' spray and dispenser which 'should' keep them out. A can of spray will last for 3 months in the dispenser so i will see how it gets on.
You can also get another solution which you mix with water and spray on the walls of the house which will stop them from landing on it.
Cost was about €100 inc delivery for all the stuff.

2. Rang a well known national extermination company and the cost was €350 for a cluster fly extermination. This included first visit and a 2nd visit a month later. It was just a kill though, not a preventative measure so I decided against it.

Mike.

Mike,
What did you get online to deal with this? My attic is swarming with them!

Mike2006

Purchased the following:

Got them from 'Pest Control Direct limited'. Not a plug as I haven't tried them yet. Should be delivered within the next couple of days and i will do the necessary over the weekend and report back.


Mike.



___________________________________________________________
DESCRIPTION QUANTITY PRICE COST

Swak Pack for Cluster Fly - 1 £40.00 £40.00
Control
No. Shipped 1

Power Fogger from Lodi 2 £6.75 £13.50
No. Shipped 2



__Totals________________________________________________________

Subtotal: £53.50
Shipping & Handling: £18.00
Total Tax: £12.51
Total: £84.01
________________________________________________________________

FlyByLight

Hi, just thought I'd add to this thread as I just found it through google. A friend of mine had a problem with cluster flies in her house, and asked me to sort it out for her. The problem is now sorted, and here is how.

First you need to identify where the flies are entering the building. This will typically be through vents in the walls or in the soffit or through any gaps between the soffit and the wall wherein the flies will enter your attic space. If they are in the attic, seal the entry points with insect wire mesh (you'll find this on ebay) that allows the vent to perform its function while stopping flies from entering and also seal any gaps with silicone sealant. As it is dark in your attic (typically), you will see light entering if there are gaps.

When you've done this, use an insecticidal smoke bomb to kill all the flies in the attic (or you can do this before you've done the remedial work if they're a nuisance and then do it again after). Then get some paper fly strips and hang them up there. These will last three months or so and will let you know through regular inspection if you've managed to seal all the entry points or not.

Now someone said that Velux windows are not a problem but let me tell you that they are. I inspected the windows in my friend's house (a dormer) and discovered that, rather than simply being a point where flies were attracted to because of the light, the windows they were actually the point at which the flies were entering her house.

Here is the problem with these windows and how to solve it. Firstly, with the wire mesh that you'll get on ebay (I couldn't find this in Ireland), cut a strip and place it over the cut-out in the Velux window frame where the handle opens the window. You'll know that there are dozens on flies in this space when you pull the handle because they all fly into the room! Staple the mesh in place at the top of the cut-out and that will stop the flies from getting in there.

So how do they get in there in the first place and how do you prevent them? Well, this is a design flaw in the window where flies can crawl under the outer lip on the Velux and get to a nice hovel for shelter in your window. But you can solve it by using a neoprene self-adhesive rubber strip (10mm x 10mm) on the top of the lip and another strip on the bottom of it. What that does is form a seal around the outer lip of the window that prevents flies from crawling in there in the first place. Did it solve the problem? Yes, and I only found this thread because I'm now wondering if I have the making of a Dragon’s Den product! You'll get the neoprene strips on ebay, by the way.

Now, you can also get pens on ebay (where would I be without it) that use an insecticide to kill any flies that crawl over the invisible mark that the pen will leave on your window frame. I used it but it wasn't necessary as the problem was solved.

The problem with cluster flies is that they breed in earthworms (yuk) so you'll find this is a common problem in rural areas. Here are a few things you can do to keep flies away from your property. Firstly, look for little gaps in the soffit where the flies will find shelter. Usually soffit is ridged so if you hit it with a power washer you'll see the little buggers coming out of all those external places of shelter. I went to the extreme of filling all those little gaps in with silicone sealant but I won't really know until next year if this keeps them away by making them homeless. The other thing I did was get cypermethrin insecticide and spray it on the soffit, gutters, external areas around the Velux windows etc and this kills cluster flies instantly (as will permethrin) and should last for a month or use before it is done again, so it also kills flies that land on the sprayed area in the meantime.

My friend was complaining about this for years but it was only when I saw how obsessive that these buggers had made her that I decided that it was a serious issue rather than just a girly thing.

The cost of all this? About 200, but well worth it as far as she is concerned. Hope this helps, and good luck!

dh0661

FlyByLight wrote: »

Hi, just thought I'd add to this thread as I just found it through google. A friend of mine had a problem with cluster flies in her house, and asked me to sort it out for her. The problem is now sorted, and here is how

Thanks for all that info.:)

DULLAHAN2

Mike2006 wrote: »

Purchased the following:

Got them from 'Pest Control Direct limited'. Not a plug as I haven't tried them yet. Should be delivered within the next couple of days and i will do the necessary over the weekend and report back.


Mike.



___________________________________________________________
DESCRIPTION QUANTITY PRICE COST

Swak Pack for Cluster Fly - 1 £40.00 £40.00
Control
No. Shipped 1

Power Fogger from Lodi 2 £6.75 £13.50
No. Shipped 2

How did you find these products?

Mike2006

Right,

Kicked off the process over the weekend.
Firstly, I just did a google search for the products online....

Used the fogger over the weekend. I vacuumed the attic space first to get rid of the 100 or so dead cluster flies that were already dead on the ground due to my daily spraying of 'raid'... I just did this so that I could see how many the fogger killed.

It seemed like there were none in the attic space as I couldn't hear their buzz.. Anyway, released the fogger and got out of the attic.
Went back up next morning and there were over a hundred dead flies on thr ground again... So the fogger works...
I am going to put the 'deterrent' spray up in the attic tonight and monitor that over the next few weeks to see how it works..

Mike.

Gulliver

Oh crap. I have this problem on our build. I thought they were just coming in between the rafters as there is no insulation or plasterboard in yet. We have 8 Velux and I believed they were gathering there for the heat.

I assumed when the house was made airtight this wouldn't be an issue, so thanks for all the info guys. I'll pay special attention to sealing and meshing the soffits and have a go at the Velux too.

darrenheaphy

I opened my velux window yesterday and had hundreds of these buggers pour in! I checked each velux and within each one there were hundreds!

Sounds like I need to look at and block each window as best I can. FlyByLight's solution looks interesting, did anyone else try anything that you can recommend?

Gulliver

I don't know if it was the weather this summer or the fact I have an airtightness membrane on but this year I've had very few (like less than 10 all year) flies in the Velux. I doubt it's the membrane as when it was really bad the buggers seemed to be getting in the grills on the Velux.

I didn't use any insecticide or seal the vents in the soffit (although they have a fine mesh on them already). Perhaps they need really good weather?

PcAngel

Mine are in sash windows. Any fine day they are trying to get out. If I open the windows loads fall from inside the frame. I'm going nuts. Any ideas as to what I can do with them?

Captain Vegetable

BnB wrote: »

When I open them, the best part of a hundred flies. . .

Beelzebub hath entered thy dwelling place and rendered it unclean!

Seekest thou a holy man of thy particular faith who willst deliver thee from yon pestilence!

2 stroke

I'm familar with these flies and have heard of them being called cluster flies, new house flies, buzz flies and zombie flies. They can appear dead when they fall out of a window, but 20 minutes later they are up and flying.
Generally I found that they were a problem in new houses but this year they are particularly bad in older houses and I've even seen them in car door seals. They seem to be attracted to certain types of rubbery seals.

MrThrifty

I just sprayed the velux catchment areas in our house this year with Protector C every few weeks from the start of August and either that or the weather conditions this year seem to have done the job. Note that we had an extremely overgrown garden last year and from research I've done, that could well have contributed to the problem as apparently the adult flies don't travel more than 100-200m from the larvae location to the hibernation point. Also, it's my suspicion now that once a fly or two start hibernating in an area, then other flies are attracted to the same place.

darrenheaphy

Protector C eh? I'll have to check that out. Did you spray outside on the tiles around the window or onto the frame itself?

PcAngel

MrThrifty wrote: »

I just sprayed the velux catchment areas in our house this year with Protector C every few weeks from the start of August and either that or the weather conditions this year seem to have done the job. Note that we had an extremely overgrown garden last year and from research I've done, that could well have contributed to the problem as apparently the adult flies don't travel more than 100-200m from the larvae location to the hibernation point. Also, it's my suspicion now that once a fly or two start hibernating in an area, then other flies are attracted to the same place.

Where did you get Protector C?

PureBred

Have same prob, not as bad as last year though. Would be interested in this product too.

MrThrifty

Sorry, held off mentioning the name of the company I got the stuff from earlier just in case I put other people/companies out. It was actually a UK company as I found they are much more aware of and on top of the cluster fly problem over there. Even some of the councils have info on their websites on cluster flies!

Anyway, the company in question was http://www.hygienesuppliesdirect.com/th/cluster_flies. However, the shipping charge was a bit steep but I think it's because the stuff has to be shipped with a courier due to it's chemical content. For example, it's listed on Amazon but they won't ship to Ireland. The cluster fly blitz kits out there will also do the job. An Irish website I just found offers these -> http://www.lambertspestcontrol.ie/index.php?page=shop.product_details&flypage=flypage.tpl&category_id=19&product_id=96&option=com_virtuemart&Itemid=71.

Note that the Protector C stuff is 'natural' in that its main ingredient is derived from some plant but it seems to be the main residual insecticide used for controlling cluster flies. There seem to be generic take-off's of it out there too, all with a 'C' in the name.

In terms of its application, it isn't rainproof (probably like most insecticides) and so can only be used indoors or in sheltered/sealed locations. It doesn't stain or mark so there's no problem if it drips on curtains or carpets etc. I spray the velux frame at the top and bottom where the flies tend to shelter and also the top part of the moving window around the lock. The flies mainly shelter and hibernate under the stiff rubber sealing strip at the top part of the frame, even if they don't always fall out when you open the window.

It's also worth spraying around general window openings between the inside and outside rubber seals if flies have hung out here in the past. Usually it'll just be windows on the sunny sides of the house (south and west) that you have to worry about. Finally, a few squirts into the attic area every now and then might be useful just to kill off any that got in under the roof tiles.

Bear in mind that despite some statements to the contrary out there, the stuff only lasts for a few weeks so respraying is necessary until the cold weather really hits. You'll still also find that the occasional fly drops out when you open a velux window but this time they'll probably be alone and dead, REALLY dead. Also, any flies that do happen to get in to your house through an open window will generally be found dead on window sills a day or two later - I presume they sample the insecticide on the way in.

Good luck with it!

beyondpassive

It helps if you can eliminate standing water around the house. Cluster flies dislike basil and mint plants for some reason, I thought they fed off something in timber but apparently their larvae are parasites which live off earthworms. uhh!

I was asked to investigate a cluster fly infestation in a group of executive houses in Dublin and the problem seemed to be in the rooflights. This was an unusual request as I am not an exterminator, but have thermography and blower door equipement for occasional energy auditing. using a pressure test we found and sealed about 40 holes in the attic rooms. the biggest problem seemed to be the myriad of recesses in the rooflight and flashings, especially around the vent. We released insectacide smoke (which the builder had) into the window frames over a period of about 10 minutes, and pushed out by positive pressure from the fans. Nasty stuff but the smoke left a residue which would prevent the fly from overwintering in the window recesses. We've since been back to do two neighbouring properties. The builder spoke to a permaculture expert who suggested planting certain plants which would attract the cluster fly's natural predator, whatever that is.

jaytobe

Mike2006 wrote: »

Right,

Kicked off the process over the weekend.
Firstly, I just did a google search for the products online....

Used the fogger over the weekend. I vacuumed the attic space first to get rid of the 100 or so dead cluster flies that were already dead on the ground due to my daily spraying of 'raid'... I just did this so that I could see how many the fogger killed.

It seemed like there were none in the attic space as I couldn't hear their buzz.. Anyway, released the fogger and got out of the attic.
Went back up next morning and there were over a hundred dead flies on thr ground again... So the fogger works...
I am going to put the 'deterrent' spray up in the attic tonight and monitor that over the next few weeks to see how it works..

Mike.

Mike and others....has anybody solved the problem fully. Got hundreds...new build, 2 velux. getting at air vents will be a nightmare...

MrThrifty

You basically need to seal or fly-screen all entry points (attic vents etc.)...

learnerplates

Same issue here.
I think they're waking up now with the bit of heat, we've had no cold so nothing killed them.

There are hundreds in the attic, only 2 or 3 on the windows so far.

What's the recommendation for attic and then the windows and house interior?


I reckon I need to take action this week as its promised nice weather.

jimf

learnerplates wrote: »

Same issue here.
I think they're waking up now with the bit of heat, we've had no cold so nothing killed them.

There are hundreds in the attic, only 2 or 3 on the windows so far.

What's the recommendation for attic and then the windows and house interior?


I reckon I need to take action this week as its promised nice weather.

have a read here http://www.ehow.com/list_7613523_oil-lavender-uses-flies.html

foxy farmer

I've spent a lot of time in attics but it's only lately I've seen these flies. The common denominator in my opinion is modern houses with the Protect membrane under the slates/ tiles. Older houses with bitumen based roofing felt don't seem to have any swarm of flies. My own attic has 2 velux windows and they collect around them from sept on. A cousin has them too. Go into the attic rattle the felt and its like a swarm of bees up there. Rotten bloody things.

r3nu4l

foxy farmer wrote: »

I've spent a lot of time in attics but it's only lately I've seen these flies. The common denominator in my opinion is modern houses with the Protect membrane under the slates/ tiles. Older houses with bitumen based roofing felt don't seem to have any swarm of flies. My own attic has 2 velux windows and they collect around them from sept on. A cousin has them too. Go into the attic rattle the felt and its like a swarm of bees up there. Rotten bloody things.

My house is a 1930's build with no protect membrane or Velux windows...

Cluster flies can be found in all sorts of properties.

learnerplates

Would multiple fly killer aerosols do the job either?

I just tried a Rentokill aerosol, 3euro, in the a garden shed (there are some cluster flies in between the timbers), I let the full can go (tied an elastic around the trigger and left it in). I could hear the buggers squirming.

Do you think multiple aerosols would do for an attic?

Ciara_Long

Hi everyone, I know this thread died last year, but I'm hoping to bring it back to life for some more advice now!!! I bought my house last christmas and into the first few months out came the flies. Last year we smoke bombed the attic but of course they all came back this year. We fogged out the attic a few weeks ago, but there are still a few flies coming in through the landing and the velux windows in one of the spare bedrooms. I think there was around 15 dead in the space of a week after fogging and spraying down all the windows. They are all dead once they come in. I've heard stories about how this cycle will just continue to repeat itself every year. I've read the thread and there are some great ideas which I will certainly try. If anyone has some more advice .... please help!!!! We are considering calling in a professional company to help deal with the problem but I'm afraid that this will just a few hundred euro and the problem will still be here next year . . . any advice or help would be great

darrenheaphy

Ciara_Long wrote: »

Hi everyone, I know this thread died last year, but I'm hoping to bring it back to life for some more advice now!!! I bought my house last christmas and into the first few months out came the flies. Last year we smoke bombed the attic but of course they all came back this year. We fogged out the attic a few weeks ago, but there are still a few flies coming in through the landing and the velux windows in one of the spare bedrooms. I think there was around 15 dead in the space of a week after fogging and spraying down all the windows. They are all dead once they come in. I've heard stories about how this cycle will just continue to repeat itself every year. I've read the thread and there are some great ideas which I will certainly try. If anyone has some more advice .... please help!!!! We are considering calling in a professionial company to help deal with the problem but I'm afraid that this will just a few hundred euro and the problem will still be here next year . . . any advice or help would be great

We didn't do anything in the end, they concentrate around the velux windows so in the last few months they spill out of one opens the window. They don't appear to reside in the actual waves. Now that summer is back they go away again!

n1st

We still have some in the velux windows too, they awoke last week. numbers are well down though.
I think there'll always be a few laying dormant in the nooks and crannies which will awake in Spring.

Thisonedone

Has anyone tried putting basil or mint plants in the attic, if so did that get rid of them?

Grogsy

OK, after reading this and a few online articles, we definitely have a cluster fly infestation here. It's the right timing of the year too and especially bad around our velux windows. Today it's like a horror movie when you open one.

One thing though, we've also started noticing a lot of little (mainly) black spots showing up randomly on our kitchen cupboards, countertops, window sills, blinds, and even around the washing machine. I've never seen anything like it before, and when you look online, it seems it's probably insect/spider droppings. They're easy to remove, so far, though not from everything. Anyone else come across this? Our house is about 10 yrs old and we've been living in it for 6. We never really used the upstairs rooms until this year so we never put 2 & 2 together about the infestation. But it has to be the flies that are making the black spots, right?

looksee

Yes, its fly - er - droppings. If you wipe them up with a damp tissue you will see they are actually brown. Just keep cleaning and concentrate on getting rid of the flies.

greek88

literally googled flies around velux and was drawn here.

We have a new build moved in only 8 weeks ago but flies are around only 2 of our velux upstairs in one bedroom only. the other bedrooms to be fair arnt bad at all the odd fly. I thaught it was the way that velux in the affected bedroom was installed maybe?We have a hatch to the attic but its well sealed from what i can see.

Do ye think my problem could be arising from the attic so and not flies entering through the vent (maybe) in the velux?
We do keep our windows open by day (nothing like fresh air in the house) but if the flies were entering by day when the windows are open i presume we would notice flies all over all our velux upstairs we have 10 but just seems to be in one particular bedroom like i said before.

any help greatly appreciated.

looksee

Flies seem to get between the inner and outer frame of our double glazed windows - if you open a window there will be a few - sometimes a lot - that mostly fly away outside. There doesn't seem to be space for them, and I have no idea how they get into the room when the windows are not opened - they are new windows and well sealed.

I found a whole lot of them in one window recently and sprayed them, and subsequently swept up the bodies. Several hours later there were more of them, dead, on the same window ledge - not any of the others. Where had they come from? How were they dead? Its hard enough to kill them with a copious dose of fresh spray, surely the spray had not remained long enough to get the next wave to come in the window? And how small a space can they get through, the windows are well sealed.