Drain Fly Infestation

There are several types of flies which may emerge from drains. Phorid flies can move through drains, commonly gaining entry through broken sewer pipes. These “humpback” flies can be an indication of a plumbing problem. Perhaps the most common drain fly is the moth fly, also called the drain fly.

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 1/4″ 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 and 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. The professional can use an enzyme to break down the film hospitable to drain flies.