The larval stage has strong jaws for feeding on fungi, bacteria, algae and other microorganisms present in moist, decaying organic matter. Larvae feed on the liquid or slime layers which develop around debris in drains, sewage treatment beds and standing water. However, when food is scarce they become cannibalistic. Following a feeding period, larvae pupate and soon emerge as adult flies. Adults live only 3 to 4 days without food, but they can survive for weeks if nectar or other liquid carbohydrate sources are available.
Adults are small and very hairy, with a pair of pointed wings.
They are frequently mistaken for small moths since the wings are held roof-like over the body when at rest. They are weak fliers and often appear to be jumping or hopping. Flight and mating activities normally occur in the evening hours when they are attracted to lights. Each female can produce about 100 eggs and , under optimum conditions, development can be completed in 2 weeks. In the home Drain flies may become abundant around bathroom or kitchen sinks.