Technically this isn't an issue of owning a home. This could happen to anyone, anywhere. Flies. Little ones. Big ones. All of them annoying ones.
I've always assumed that flies hatched from eggs that piggy-backed on fruit and other unsealed containers you bring into your dwelling. I recall reading that there are species of flies that reproduce by parthenogenesis - no males required. None of that is important. Once you have a fly infestation, you need to deal with it for many generations of flies.
This is not my first rodeo. (Cue the horsefly joke.) I have several of those electronic tennis racquet bug zappers. It's very satisfying to swing and hear a loud "SNAP!" when you catch one. What I've found more effective is to pour some apple cider vinegar in a bowl and lay the paddle zapper horizontally over it. The flies try to get at the ACV and die trying. It's more passive, but it works.
On the passive front, I've purchased three hanging bug zappers since moving in. One is still working. It kills anything up to moth size, but the smell of frying bugs can be annoying, too. The documentation says the lone working zapper is specifically for mosquitoes and will not attract flies. Tell that to the crispy dead flies.
Just as passive are fly strips. Fly strips are ugly but require no power. I have several hanging around.
The next approach is chemical warfare. Numerous companies produce sprays that contain nerve gas or something similar to get rid of every bug known to man. I may end up buying some, but first I've ordered Zevo spray. "Uses a Powerful Blend of Mint and Rosemary to Kill Bugs on Contact."
