Black Flies In House In Winter. Excessive dryness outside drives these tiny black flying bugs inside homes while they’re searching for a more temperate place to live. Gnats are tiny and black, resembling mosquitoes to an extent, and they bite too.

These flies are easy to tell apart: Sightings of gnats near windows are pretty common in the gnats months when they try to get inside homes. Why are there black flies in my house in the winter?