Drain Fly

  • Common Name(s): Drain Fly, Moth Fly, Filter Fly, Sewage Fly, Filth Fly
  • Order: Diptera
  • Family: Psychodidae
  • Common Species: Psychoda spp.
  • Commonly Confused With: Insects from the Order Lepidoptera–Butterflies and Moths


How to Identify?
Drain fly adults vary from brown to gray to cream in color, and they possess colored hairs on their wings and different sections of their body. They look like teeny tiny moths flying around the home. The larva, pupa, and eggs will probably never be seen by the homeowner. Adult drain flies range from 1.5 to 5 millimeters in length.


Where do they live?
Drain flies live in drain scum on the inside of pipes (sinks, showers, floor drains) as juveniles. Usually, they are found in bathrooms around the home. They can also be frequently found in public restrooms, locker rooms, and sewage treatment plants. Outdoors, they are not the best at flying and can be carried quite some way by the wind. Inside, adults are commonly seen on walls around restrooms or areas that contain a drain in the floor or decaying material because this is where they prefer to lay their eggs. Outside, adults will breed on any natural decaying organic material, gutters, and storm drains.

Food Source

What do they eat?
Adult drain flies feed on nasty polluted water or on flower nectar. The larvae feed on bacteria of fungi of the drain scum or the other decaying organic material in which they are living.


What do they do?
These insects are most active later in the day, and they are attracted to lights. Since juvenile drain flies live in the scum on pipes and other unsanitary conditions, the adults are often seen congregating near these breeding areas. While drain flies pose no immediate threat, they are a nuisance in the home and, due to their breeding and living near unsanitary areas, pose the possibility of being mechanical vectors of disease. A disease is considered to be mechanically vectored when it is transmitted by contact: a drain fly lands on drain scum, picks up bacteria on its body, lands on your toothbrush, food, etc., and the bacteria is transferred by the fly to whatever item it lands on; mosquitoes transfer viruses, bacteria, etc. through a bite, which makes them chemical vectors.

Fun Fact

While drain flies may look like moths, they are not actually in the Order Lepidoptera–Butterflies and Moths. They are in the Order Diptera, which includes biting and non-biting flies such as mosquitoes and house flies. Flies can be easily differentiated from moths and butterflies by the possession of halteres (flight stabilizers that look like small maracas underneath the wings) and only possessing one pair of wings.

Additional Resources

The first link is for the Psychodidae family as a whole. I provided the second link, which is for the subfamily of drain flies since drain flies share a family with an insect called sand flies, which are blood-feeding insects.


Author: G. Wyatt West– B.S.E.S University of Georgia 2017; Board Certified Entomologist

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