Size:
Range from 1/6 to 1/4-inch in length.

Behavior:
Drain flies tend to live and reproduce in areas of shallow, polluted water, laying their eggs in the muck and gelatinous film or residue that accumulates on the sides of drains in homes or on septic tanks and in sewage disposal areas. Larvae hatch quickly (32-48 hrs) and their complete life cycle can be completed in 1-3 weeks. Adults live for about 2 weeks, with old ones dying and news ones emerging to take their place.

They feed on organic matter and microorganisms, on polluted water and flower nectar. Adults stay in shaded areas near plumbing fixtures and on the sides of tubs and showers during the day. Most drain fly activity occurs during the evening when they hover in and around drains and sinks.

Drain flies breed in large numbers at sewage filter plants (and are sometimes referred to as “sewer flies” or “filter flies”); they can be carried by the wind to homes up to a mile away where they are small enough to pass through window screening.

Habitat:
In homes, drain flies inhabit sink, bathtub, shower, or floor drains, especially those that are seldom used, have standing water, or caked with organic buildup. They can also be found around other perpetually moist areas under dripping pipes and refrigeration equipment. They can also be found around the organic debris found in sewers, septic tanks, drains, wet brooms and mops, even the soil close to a leaking or ruptured plumbing line.

Health Concerns:
As they are common inhabitants of sewage treatment plants and other similarly bacteria-infested environments, there is the possibility of pathogen transmission and contamination of areas they come in contact with. Bronchial asthma can occur by inhaling fragments and dust of dead flies.

Control:
Control of drain flies should be aimed at control of the breeding sites. The most effective control method is to clean drain traps with a stiff-bristled brush, removing all the slime in which the flies breed. It may be necessary to remove the trap to thoroughly eliminate the debris they use for breeding. Pouring hot water down the drain provides short-term control; Drain fly larvae are difficult to drown since they are able to trap air bubbles and remain submerged for a day or more.

Clean dirty garbage containers, and eliminate wet lint from under washing machines as well as standing water in containers under houseplant pots. Outside the home, inspect A/C units, birdbaths, and other sources of shallow, stagnant pools of water where breeding may occur.

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