Drain flies are small and have light-colored wings, and they're considered to be part of the gnat family. The wings of a drain fly have many scales, so when killed, drain flies produce a small dust cloud. It's common to find drain flies resting on ceilings and walls, and if bothered, these gnats will hop and make short flights to new resting locations.
In many situations, drain flies cause a temporary problem. Since these flies are known to breed in standing water, it's common for homeowners to find a drain fly infestation after coming home from a vacation. Drain flies don't breed in moving water, so regular household activity helps to keep them away. A typical drain fly can be 1.5 up to 5 mm in length.