This is my first time living in an apartment in the summer. I'm living in New York City. Every day, we spot a new fly, and we kill it.
I can't detect how flies are entering my apartment! My husband and I have watched each other opening and closing our main door when we leave and return home — we see no flies. Is it possible that flies are flying through the exhaust duct in our balcony, and entering through the kitchen fan? Can we rule out the possibility or not? See below — our Sakura R-727II doesn't have any filters.