Psychodidae, also called drain flies, sink flies, filter flies, sewer flies, or sewer gnats, is a family of true flies. Some genera have short, hairy bodies and wings, giving them a "furry" moth-like appearance, hence one of their common names, moth flies. Members of the sub-family Phlebotominae, which are hematophagous (feed on blood), may be called sand flies in some countries, although this term is also used for other unrelated flies, such as horse flies (Tabanidae) and no-see-ums (Ceratopogonidae).

There are more than 2,600 described species worldwide, most of them native to the humid tropics. This makes them one of the most diverse families of their order. Drain flies sometimes inhabit plumbing drains and sewage systems, where they are harmless, but may be a persistent annoyance.

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