Drain Flies are small flies about 1/8 of an inch long, they appear fuzzy, they don’t fly very well, and are sometimes called moth flies, or sewer flies. As the name suggests these flies often are found around drains. Today we treated a commercial public rest room that had about 20 of these guys flying around. The drain that they were breeding in was a overflow floor drain in the handicapped stall. The drain is rarely used and provided excellent harborage for them. Prevention of these small pests would include keeping drains clean, and using the drains frequently.