The Drain Fly or Moth Fly is a common name used for the members of family Psychodidae, in the fly order Diptera. They are small, about 4mm long, moth like creatures, found in damp habitat. Its color varies from gray to dark gray. It got its name drain fly, because it grows in drains and the name moth fly, because of its moth like appearance. Drain fly is a nuisance in houses and buildings. It can also be found near the compost bins or dirty trash. It's also know as Bathroom Fly.