We're being invaded!

It used to be the Asian beetles that look like their much more docile Ladybug cousins, now it's house flies!

Each fall for the past several years we've dealt with literally swarms of the Asian Beetles all over our house. This year, for some reason it's been the (way too) common housefly. The other night I killed 12 on the downstairs window and then another 8 upstairs while watching TV.

I can't find the source! There is nothing that is acting as a breeding ground that I can find. While there may a loose screen or something somewhere in the house that would provide a doorway for them, I'm not sure why they seem to be swarming right now. No drastic weather change. No rotting corpse that I can find (or smell).

I just don't get it!