Moth Fly

Common Name: Moth Flies / drain flies / sewer flies
Scientific Name: Psychoda species (Family Psychodidae)

Introduction. These flies get the common name of moth fly from their fuzzy appearance, their bodies and wings being very hairy. The drain fly and sewer fly common names are from places or situations, which represent typical breeding and developmental sites. Although usually thought of as nuisance pests, there have been cases where inhalation of their body parts caused bronchial asthma. Moth flies are found throughout the United States and most of the world.

Recognition. Moth flies are 1/8 to 3/16 inch long, delicate and fuzzy. These flies have broadly oval, hairy wings that are held roof like and outward from the body while at rest. The antennae are long and fuzzy as well.

Similar Flies. Other flies lack the dense fuzz on the body and wings.

Biology. Female moth flies / drain flies lay their 30 to 100 eggs in irregular masses on the surface of the gelatinous film which covers filter stones of sewage treatment plants or which lines moist portions of drain pipes. Both the larvae and pupae live in this gelatinous film with their breathing tube projecting through the film. The larvae feed on the algae, bacteria, fungi, microscopic animals, and sludge of this film. At 70°F eggs hatch in 32 to 48 hours, the larval stage lasts 8 to 24 days, and the pupa stage lasts 20 to 40 hours. The developmental time (egg to adult) is 7 to 28 days, depending on conditions. Adults typically live about 2 weeks.
Although they may breed in sewage, apparently they do not transmit human diseases. However, there have been cases of bronchial asthma where the inhalant allergen consisted of dust composed of dead moth fly body parts.

Habits. Moth flies are weak fliers, so indoors they are usually seen resting or crawling on the walls or other surfaces. When they do fly, it is only for short distances of a few feet and their flight is in characteristic short, jerky lines. During the day, they typically rest on vertical surfaces near drain openings indoor and in shaded areas outside. Their peak activity is in the evening when they can be seen flying or hovering above drain openings indoors or sewage filter beds, etc. outdoors.
Typically, only a few adults are seen at a time in structures because the adult flies live only about 2 weeks but are continually being replaced with newly emerging flies as they die. However, large numbers of adults usually means that an outside source such as a sewage treatment plant is involved. Even though they are weak fliers, they can be carried to distances of 300 feet or more by the wind.

Cultural Control & Temporary Measures. After proper identification and a thorough inspection by a Rottler pest management professional to find the breeding sites, conducive conditions found in these sites must be addressed via mechanical and chemical cleaning processes. Places to clean include: slimy drains, sewer leaks or backup, dirty garbage cans, saucers under potted plants, bird baths or feeders, clogged roof gutters, clogged storm drains, air conditioner drip lines, cooling tower drains, moist compost, rain barrels, and septic tanks. If large numbers of flies are seen outdoors, a nearby sewage treatment plant may be responsible, especially if upwind from the structure. In relatively new structures, drains can often be cleaned out using over-the-counter drain cleaners followed by very hot water. If this is not successful, mechanical cleaning of the drain with a stiff bristle brush is required to remove the gelatinous film lining, and this should be followed with a caustic drain cleaner.

Professional Control. A Rottler technician can reduce or stop breeding by moth flies via the repeated use of appropriately labeled botanical, microbial and/or enzymatic insecticides and insect growth regulators in floor drains, waste water traps and other breeding sites. Strategically-placed scent lure jar traps and insect light traps (ILTs) can be installed by a Rottler technician to reduce numbers of adult moth flies indoors. A non-residual aerosol insecticide can also be used to kill large numbers of adult flies, but only the elimination of the breeding sites will provide long-term control.