Drain Fly

Characteristics: Small flies with moth-like appearance.


  • Breeds in sewers, floor drains, basements and washrooms.


Drain flies, also called moth flies, belong to the family Psychodidae and get their name because they often breed in drains. They are found throughout the United States and can become an annoyance in homes, sometimes appearing suddenly from sinks and bathtub drains. They can breed in tremendous numbers in sewage treatment plants and then be carried away by the wind to nearby buildings, where they can crawl through ordinary fly screens.

Drain Fly Habitat

Drain flies develop in muck or gelatinous material that accumulates in sewage disposal beds, septic tanks, moist compost, or dirty garbage containers. They may also emerge from drains of sinks or bathtubs, from tree holes, rain barrels, moist organic solids, or bird nests which have accumulations of fecal material. Drain flies gather, mate, and lay eggs in moisture or standing water. The slimy film that forms in sewers and drains is a favorite breeding spot. Inside structures, they are strongly attracted to light and will be found on glass windows, doors, lamps, and around indoor lighting.

Drain Fly Behaviors, Threats or Dangers

Drain flies do not bite people or animals or do damage to structures or plants. However, because these flies originate from filthy sources, they have the potential of being mechanical vectors of diseases. Populations of these insects can become a nuisance in homes, and their presence is almost always linked to a clogged drain. In residential homes, the most common breeding sites are bathroom drains. Drain flies are weak fliers and when encountered, they are often found crawling on walls and other surfaces.

Drain Fly Prevention

The key to preventing a drain fly infestation is to eliminate their breeding sites. Since these flies are drawn to drains, keeping your drains as clean as possible will prevent breeding and new eggs from hatching. With regular cleaning and careful attention, most drain fly problems can be fixed within a week. Scrub sinks once a week with a cleanser and pipe brush around and inside the drain. If necessary, use drain cleaner gel once a week to keep organic matter from gathering in drains. Drain gel should be applied when the drain will not be used for several hours, usually at bedtime.