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A source for information on flies

Drain Fly   Family Psychodidae


About 1/16-inch long with a light gray or tan body and lighter-colored wings. The body and the wings are covered with long hairs, giving the fly a fuzzy appearance. When at rest, the wings are folded over the body in a characteristic roof-like manner. Drain flies are grayish or brownish-black in color, with the body and wings covered with hairs. Their large wings cover their body, giving them a moth-like appearance when still, and are sometimes called “moth fly”.

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

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.


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. Adults are found on bathroom, kitchen or basement walls. More active at night, do not bite and, surprisingly, do not transmit human diseases.
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. They do not bite and, surprisingly, do not transmit human diseases.


Organic matter and sewage.


Eggs are laid in irregular masses almost anywhere decomposing organic materials are found. Under favorable conditions, the flies can go through one generation in as little as one week. Two to three weeks is more typical.

Drain Fly Facts:

The common drain fly, or Diptera psychodidae, has become an integral part of many water-based ecosystems. However, drain flies pose problems for homeowners if the population grows excessively. Drain flies are common in moist areas coated with nutrient-laden organic material. As their name implies, they are found in house and storm drains. They can also be found near decaying logs and compost piles.

Drain Life Cycle:

Drain fly eggs hatch into white, nearly translucent larve. These larvae have been known to survive dramatic temperature swings and low oxygen levels. They are sometimes found thriving beneath layers of biodegrading organic material. In small numbers, drain fly larvae are considered beneficial because they break down materials that cause drain clogs. Drain fly larvae have extremely strong jaws and are capable of cutting through layers of dense slime and build-up.

Drain Fly larve pupate and emerge as mature adults with six legs, a pair of wings and antennae. Adult drain flies usually live about two weeks, but newly emerged adults rapidly replace them. Adult drain flies are also known as moth flies due to their appearance: they are small and furry with large, ovoid wings and prominent antennae.

Drain Fly Control:

The best control for these flies is to remove the breeding site, which is the organic material that collected in the drain. If these flies are present in the house there is almost certainly a slow or clogged drain. Find the drain and physically clean it out. All the liquid drain cleaner in the world will not solve the problem, you’ve got to physically remove the material causing the clog. Once the material is removed (along with the larvae) the problem is solved, except for the adult flies. They will live about 20 days, but since they will have no place to lay eggs, the problem will disappear when they die. 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.

"Riley Pest Management is a small company with a big heart that will go the extra mile to take care of an issue for you no matter when it happens. They have proven to be a very good friend to non-profits."

-- Duggan Cooley, former CEO- RCS

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