Larvae of drain flies are legless, about 3/8 inch long, wormlike and gray, with both ends somewhat darker. Adult drain flies are small (1/6 to 1/5 inch long), fuzzy, and dark colored insects. Their bodies and wings are densely covered with hairs. Because wings appear large for their body, are held roof-like over the body when at rest, they are often mistaken for moths. They are not strong fliers and fly only a few feet at a time.
Drain will need to be cleaned. It is best to remove the drain trap and use a long stiff brush to dislodge the gelatinous material in the drains. Then, flush with boiling water and bleach to remove any residue.
Drain flies are common around sink drains, sewage treatment facilities, storm drains, dung and rotten vegetation. They feed on bacteria, fungi, algae and other microorganisms present in decaying organic matter. Drain fly larvae are difficult to drown because they are able to trap air bubbles and remain submerged for a day or more.