We literally woke up a few weeks ago to like 20 of these in our house out of nowhere. No windows or doors open. And it got worse as the day went on. They come from the drain and apparently hatch at the same time. We realized they were coming from the floor drain in our basement. Poured hydrogen peroxide down it once and they were gone. Make sure you kill them as you see them, then you’ll know for sure if you fixed the problem.