Each year, PCO's receive calls from homeowners who have small, moth-like insects on the walls of their bathrooms, kitchens or in the basement. They generally turn out to be moth flies. These flies do not bite and are of no economic importance. Even those which breed in sewage beds apparently do not transmit human diseases. These flies are a nuisance, though, in both homes and sewage disposal plants. The adults can become so numerous around disposal plants that they plug filter beds, intakes and drains and get into the eyes, ears and noses of workmen in the area.