Number 65 • June 30, 2009 • Jeffrey K. Barnes

Moth flies, drain flies
Order: Diptera
Family: Psychodidae
Genus and species: Psychoda alternata Say and others

Moth fly

Moth flies are very small flies covered with a furry coat of fine setae that renders a resemblance to tiny moths. Outdoors, adult moth flies are usually found in moist, shady areas and in the vicinity of sewage filter plants. Indoors, they may become pests in bathrooms, kitchens, locker rooms, and other areas provided with water service and drains. Larvae of most species in the family Psychodidae live in moist or wet substrates. The most common pest species in the eastern United States is Psychoda alternata. It is about 2 mm long, has a light tan colored body, mottled wings and 13-segmented antennae. Larvae live the gelatinous material that covers filter stones at sewage plants and the insides of drain pipes and overflow areas of indoor plumbing. They feed on decaying organic matter and microscopic flora and fauna. In infested buildings, adults are often found resting on walls, frequently in showers. Determining where the flies are breeding and removing the scum in the pipes or other moist areas should lead to satisfactory control. The insides of pipes should be scrubbed to remove the gelatinous material. Caustic drain cleaners and household insecticides are not recommended as effective control measures, and they could be damaging to the environment.