Drain Fly

Facts, Identification & Control

Latin Name

Family Psychodidae


Drain flies measure about 1.5 to 5 mm 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 drain fly folds its wings over the body in a characteristic roof-like manner.

Behavior, Diet & Habits

In homes, adults are found on bathroom, kitchen or basement walls. More active at night, drain flies do not bite and, surprisingly, do not transmit human diseases. Drain flies feed on 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.

Usually, the homeowner never sees drain fly larvae since the larvae are located in the gelatinous film inside drains. However, sometimes, when drains are taken apart, larvae can be found in the film.

Drain fly larvae are not longer than 4 to 10 mm when fully mature and they are slender with a dark strip on the “back” or dorsal area. Larvae do not have eyes, and they are legless. On one end of the larva, there is a dark breathing tube used to extend out of the film to obtain air.

After the larvae mature, they will pupate or rest until they emergence as adults. The adult is the only life stage usually observed. Drain flies, even though they live in filth, are not known to spread any disease to humans.

Signs of a Drain Fly Infestation

As with most flies, the most noticeable sign of drain flies are the adults. They typically are seen resting on the walls in bathrooms or near the breeding materials. Larvae also may be observed wriggling in the breeding material.

More Information

The common drain fly, or 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 fly eggs hatch into white, nearly translucent larvae. 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 larvae 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.

Additional Drain Fly Information

Schedule a free pest control inspection for more prevention and treatment suggestions.