Drain flies aka sewage or moth files are only about 1/8th inch in size and are black or brown.  What identifies these small flies is the unique pattern of veins in its wings.   Their bodies are covered with hairs and when crusted it leaves a powdery smudge.  Drains are the most common places these flies can be found.  Understanding the different breeding sources for the flies will help you identify and manage the infestations.

Breeding Sites

These flies like to breed in drains which is a good place to start inspecting.  They live off the debris on the side of the drain and in the trap.  Its a humid film from the larvae.  A quick tip to know if you have drain flies.  Place tape over the drain and cut come holes in the tape.  If you have files they will get stuck in the tape as they try to leave the drain.

Slab Floors:  They like to breed in the organic debris under the slap.  Adult flies will enter the living space above the slab through cracks and then back thru into the drain pipe.  To determine if there coming up thru the slab place masking tape over the crack as described above.  If drain flies are breeding under a slab then a hole must be broken through the slab to see if a pipe has broken and if flies are breeding.  After a hole is broken through then dig in the soil under the slab and inspect.  An adult’s larvae could be deep into the soil.

Sump pits and Sewers:  Sewer and pump pits need to be checked for activity even if its not close to where the moth flies have been flying.  Also its a good idea to inspect the pits of elevators for excess water or moisture.  In homes, drain flies are found mostly in bathrooms drains.  Shower pans are prone to leaking and the area under the shower pan becomes a prime moth fly breeding source. Remove all organic debris trapped in small cracks and crevices under the legs and bottom edges of kitchen equipment. The debris needs to removed, thoroughly dried and a long lasting caulk applied to seal the crack.

In Your Home:  Dirty garbage containers and standing water in containers under houseplant pots. Outside the home, inspect air conditioners, bird baths, shallow stagnant pools of water and sewage treatment facilities upwind as adult flies will travel with the wind.  Drain flies may also breed in moist, shady areas outdoors such as under potted plants, in bird feeders and baths, in moss, in clogged roof gutters, under air conditioners, in thick mulch, or on wet ground areas.

In natural settings, sewage fly larvae feed on decaying plants and animals. Most drain flies are harmless to humans, though they may transmit bacteria and other microorganisms from their breeding sites to areas where people are. Moth flies do not bite. Adults live about two weeks