I have no dead animal, that I know of. We do have a creek running behind our house and saw roof rats so we set out poison but these flies were here about two weeks ago and all the sudden today I've seen four! Seriously, it's irritating but not as bad as above. My cat loves them but they're more than annoying me!

Turn the A/C colder...they will get even slower..

Does the house smell a little funny, too?

I have that scene from Karate Kid in my head...what you need is Mr. Miyagi and his chopsticks.

Or an efficient crane kick. Sweep the leg - finish him.

No. I don't think it has anything to do with a dead animal UNLESS you have a bad smell. I did not....and I too had new windows! This is the second time it's happened. It's freaky. Ill!! Yuck! Shiver!!! I just wipe there lazy asses into paper towel and kill them all! Yuck!!

If there's no smell it's the window void thing. I've been watching but haven't caught them coming in yet. I'm killing 20 at a time!! Ewwwwww....

Yes, you need to get rid of the attraction, but to catch the ones that are leaving the dead animal, you can make a fly jar for your house. Take a jar with a metal lid, cut an X in the lid (use a sharp knife, put the point on the lid and then tap the handle until the knife sinks in, repeat until you have a small X). Use a screwdriver to bend the leaves of the X down and pointing into the jar. You want the whole opening to only be about 1/4 - 1/2 an inch diameter, so not too big. You want the flies to be able to get in, but not get out. Fill the jar about 1/2 with water. Use a knife put some molasses or sweet and fragrant jam (cheap strawberry preserves work well) on the inside of the lid, spread it thick. Put the lid back on. Leave the jar out somewhere where you can watch it (and know when to switch it out). The flies will smell the bait, will fly/crawl into the jar, they won't be able to get out and they will end up in the water, drowning and dying. This will control the flies that are flying around. You can empty the jar outside in the gutter, rinse and restart or just use a new jar.

After the dead animal is gone, the flies will stop and you can get rid of the fly jar.

We've had one or two a week the last few weeks, and I'm pretty sure they're flying in the doors when my kids dawdle with the doors open... There is one flying around me right now, actually -- very gross -- and I have a towel at the ready to snap it... I've found when the weather is nicer, they'll fly right out a door if you open it. Today, when it's hotter and humider and we have the AC on (don't judge...), the sucker won't leave.

If you have a BUNCH, yes: dead animal. We had that once growing up and LORD it was gross. We ran around swatting and vacuuming up flies in the master bedroom all night one night. Ugh. Some critter had died in the wall.

I love your title

It sounds like the opening of a new sci fi film.

Be careful. Flies can turn into maggots!

dead in the wall no doubt --- u can live in a mansion / castle with 45 helpers richie rich n the mice will find the way --- yes ..... really

Really ? We have had this and it seems to happen around this time of year...they will fly in when a door is left open and I think they are looking for cooler temperature of the house to......lay eggs. I think these flies, fly slowly because they are pregnant. fly swatter is how we deal and I become very strict about keeping doors closed.... We live in very clean large house in nw dc. Maids come 2 x per week.

dead mouse in the walls. They will go away when they eat it all.

I am having dry heaves right now. Trying to think happy thoughts! *swallowing* *swallowing* *swallowing*

Gross

Slow flies are soon-to-die flies. They are running out of food. You have eggs and maggots somewhere -- probably near your trash cans. Get thee a vacuum cleaner and vacuum up those suckers.