Every summer at night when we have curtains up and turn on the indoor lights, a large number of small insects (moths, small beetles, spiders, other slim thin-legged insects, etc.) will manage to find their way inside. This happens despite that the (double-hung) windows are closed. The situation is much better if the lights are out or if the curtains fully cover the windows. On the other hand, even if we block the lighting, the insects can still come in if the windows are open. As a result, our summer becomes pretty miserable, choosing between temperature and bugs..
This happens in every room of our two-story house and I certainly checked that the window screens are intact or patched up. I suspect that there might still be small gaps between the screen frames and the window sills and the lighting or human smell may be what is attracting them.
Since physical barrier isn't working, is there some spray solutions that are safe end effective to use?
We live in Greenfield, MA, if that matters. And it does not look like this post provides solutions for our problem.
UPDATE I have used a thermal camera to find cracks. The only cooler spots (in winter) are where walls meet the ceiling but there are no visible opening. I also suspected that the bugs come in through wall cavities (e.g., outlets) where vapor barrier is not continuous, but it is curious why closing the windows and curtains would help if this was the case.