Drain Fly Infestation
The drain or moth fly is named because of the scales on its wings, similar to a moth. When touched, these yellow to gray or black scales will come off, leaving a residue. The moth fly is small, typically less than 55 mm long.
This fly lays its eggs in the drain on the gelatinous material which normally forms around the inside of drain lines. Larvae emerge from the eggs, and the cylindrical larvae will extend breathing tubes through the film for air while feeding on the microbes inside the drain.
Adult drain flies emerge, typically when warm conditions exist. These flies are not excellent fliers, and the flying pattern appears to be jerky and irregular. Rarely does the homeowner see the full infestation of these flies; more likely, only adults are observed.
The best way to control drain flies is to control adults and to keep the drains clean using periodic cleaning. A pest control professional can use an enzyme to break down the film that is hospitable to drain flies.