The insect family Psychodidae (known as “moth flies” or “drain flies”) are small flies with short, hairy bodies and wings giving them a “furry” moth-like appearance. The adults have long antennae and the wings are leaf-shaped, either slender or broad. Adult drain flies are typically nocturnal and associated with damp habitats. The larvae and pupae live in the thin film found in drains and septic tank field lines and on filter stones. The larvae feed on fungi, bacteria, algae and other microorganisms found in the liquid or slime layers that develop around debris in drains, sewage treatment beds and standing water. Outdoor areas include: damaged or faulty septic lines; areas where rainwater tends to pool or air conditioning condensate lines; beneath air conditioning units on the roofs of commercial buildings. Indoor areas include: toilets (particularly if they are not used frequently); sink and bathtub/shower drains; floor drains in commercial buildings and basements; condensate lines for icemakers; and loose ceramic floor tiles where water may collect.

Adult drain flies are small (1/6 to 1/5 inch long), dark, and densely covered with hairs. They hold their large wings roof-like over the body when at rest, giving them a moth-like appearance. They are weak fliers and fly only a few feet at a time. They are most active in the evening. Both mated and non-mated females lay eggs. Egg masses contain 30 to 100 eggs, which hatch in less than 48 hours. Adults live only 3 to 4 days without food, but can survive for 1 to 3 weeks if nectar or other liquid foods are available.