Flies in house coming from nowhere
At least once a year, we are invaded by flies. We have no pets or fly attractors and the kitchen is clean. Although the windows are screened and the doors aren't left open, we get about 20-30 flies per day inside the house. Usually this happens once in the summer and it happened this summer. It's late November and it's happening again. This morning, I left to go to the drug store and, when I returned, there were about 10 flies buzzing around looking for a way out. We don't have a basement and they don't seem to be coming from anywhere in particular. The flies stop coming after about 5 days but it's disconcerting. About 15 years ago, the flies were large and slow moving. For the past 15 years, they look like regular house flies.
I searched this forum and saw one post saying that the large, slow moving flies were cluster flies looking for a place to hibernate. We don't have them any longer. Does anyone have any insight about the house flies we have now? We usually let them out or swat them. I'm wondering if there's a way we can stop the cycle. Thank you.