Drain flies (Psychodidae: Psychoda spp.): Also referred to as moth flies.
Oblong or oval, appears moth-like, and is about 3/16 inch, wings fuzzy. Larvae up to 3/8 inch.
Habits: Commonly found in bathrooms (breeds in scum in drains, showers, overflows, toilet bowls, etc.). Adults rest motionless on walls until disturbed, and then fly well. Need wet conditions to breed. When toilets have gone un-flushed for an extended period, moth flies may lay eggs in the toilet tank, and larvae can be found there. When the toilet is finally flushed, larvae can make their way into the toilet bowl, where they are discovered.
Interventions: Clean the inside of the drain of all scum and detritus using a mild cleanser and a bristled brush. Never pour insecticides into drain. Pouring bleach into drains is not effective. Make certain that the water trap in the drain line (especially common in less frequently used sinks) is filled – if the water trap dries out, flies and other pests that live in the drain lines will be able to enter the building. To help determine whether a particular drain is infested, place a clear cup,
inverted, over the drain. If flies emerge from the drain, they will be trapped by the cup, and can be seen.
Might Be Confused With: fungus gnats, humpbacked flies, fruit flies, and small moths.