Drain flies, also called Moth flies, are small flies with short, hairy bodies and hairy wings that result in a ‘furry’ or moth-like appearance. They have leaf-shaped wings, with very rudimentary wing venation (the simplest of any known fly). They are typically nocturnal, and require damp habitat to live in. The larvae are aquatic to semi-terrestrial, and so can become a major nuisance in bathrooms and basements, outdoors around sewage areas, or just anywhere where water and drains go hand-in-hand together.
Additional Information (with management recommendations): Drain Flies (Ohio State University)