Drain flies, also known as sink flies, sewer flies, moth flies, or sewer gnats, are tiny insects from the Psychodidae family. The family includes more than 2,600 species worldwide.

Adult drain flies typically measure 2–5 millimetres long. Their grey, tan, or dark-brown bodies and wings are covered in fine hairs, giving them a fuzzy, moth-like appearance. When resting, they hold their broad wings over the body in a roof-like shape. Their flight is weak and fluttery, so they are often seen resting on bathroom walls, near sinks, or around floor drains.

These insects usually breed in the slimy biofilm that develops inside drains, pipes, and other damp areas. The film contains decaying organic matter that provides food for their larvae. Simply spraying adult flies may offer temporary relief, but it will not solve the problem if the breeding site remains.

In this Australia-focused guide, you’ll learn how to identify drain flies, understand why they keep appearing, assess potential hygiene concerns, and remove the conditions that support them. Cleaning the drain and carefully eliminating organic buildup are important first steps. If the infestation continues, professional fly pest control can help identify hidden breeding sites and recommend suitable treatment and prevention measures.