Now is the transition from spring to summer. The house I am now living has some strange things happening.
In the daytime of one day last week, I found many flies gather on the inside face of the window in the front living room. I then opened the window and drove them out. The next day, I found there were still many flies again on that window. Same thing happened again and again in the past week. Besides that window, there are also some flies flying elsewhere in the first floor. At nights they gather around our lights. I remember same thing happened in last year's summer as well.
The windows and doors are either closed or have screen on. I cannot think out of some possible way for the flies to come in. There was an envelop slip on the front door, but it was by default closed, unless people from the outside want to deliver some mails to the inside. There was also a pipe stretching from the basement to the outside, for letting out vapour of heating during winters.
I wonder if this kind of things has happened to you guys as well? Where can so many flies come from?