By Debra W.
I once had flies inbetween the panes of glass on a window. Luckily, they were not sealed panes, and I could take the inner one off to get rid of the flies. Who knows how they get in? Not me! I suspect that flies can crawl into spaces and "hibernate" in the walls, and then crawl out at the oddest times.
House flies will not be breeding in your trash can or around your pet's food unless your house is full of something like rotten meat, which I seriously doubt. House flies have a fairly long life cycle - egg, maggot, pupae, and then adult fly. You'd certainly have noticed maggots somewhere I think. Your flies have likely come from outside somehow, and been laying low inside the wall,. Makes them sound like little spies, but that seems to describe their behaviour! LOL
It might be that a fly has laid her eggs somewhere in your house and they've all reached maturity. One time I was absolutely swarmed with fruit fly-like bugs in the thousands (or it seemed to be!). I've never seen so many bugs. It turned out they were coming from the trashcan. I cleaned it out well under the lid and the bugs all soon died.
Maybe have a good clean around any potential food sources, cleaning out trash cans and areas where pets eat, things like that. They should be gone within a few days. If they're on the glass door they might actually be trying to get out, so you might have luck shooing them outside. Fly strips or traps might help too and be better for your lungs than spraying. Good luck!
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