Have you been finding lots of small, dark flying insects on your window screens or even inside on the window sill? If so,you may be seeing Hackberry Psyllids, sometimes called Hackberry Nipplegall Makers. These insects develop on the leaves of hackberry trees and in the fall when the weather becomes cooler they may try to enter homes to escape the lower temperatures. These small flies are small enough to pass through some window screens but are not harmful and do not do any damage to homes or property.
Removing nearby hackberry trees is a solution but it is not a very practical one. Physical removal is the best way to handle these annoying flies. On the exterior you can spray the house/windows down with water occasionally. Inside, vacuuming is the best way to deal with them, however if you do nothing they will just die as a matter of course. Pesticides are not usually recommended as they aren’t really effective and can make a mess of the screens and windows. They are especially attracted to light colored houses as well as lights on at night. Once the temperatures drop consistently you should no longer see them.

Hackberry Psyllids eggs on a hackberry leaf