Physical Characteristics

The adult stage of this tiny, hairy fly (order Diptera), which also is known as the moth fly, filter fly or sewage fly, ranges anywhere from 1/16 to 1/4 inch in length. Depending on the species, it can be pale yellowish, brownish gray or black. Wings are oval and fan outward 45 degrees or so; antennae are segmented and furry. The mature drain fly larva is 1/8 to 3/8 inch long, slender and wormlike, with no legs, and with pale coloring except for darker lateral bands on top.


Drain Fly


Drain flies are tiny, which means they can penetrate screens and get inside structures easily. They’re weak fliers, although they can be carried by wind currents for up to 100 yards – the length of a football field. More commonly, you’ll find them resting inside on walls or near drain openings, and outdoors, in the shade. Often, their appearance is noted by their sheer quantity – a lot of them at once, clustering on lampshades, windows, sinks and floor drains in showers indoors, and outdoors in clogged roof gutters and storm drains, birdbaths, moist compost, potted-plant saucers, weed clusters and, if you live near them, sewage ponds. Drain flies represent a health hazard, because when inhaled, they have been linked as a trigger of bronchial asthma. Their lifecycle, from egg through pupa, can range from 10 to 28 days, and adult drain flies live for about two weeks, with dying flies being replaced by emerging adults if favorable conditions persist. The larvae feed on fungi, sludge and microbes on the filmy surfaces of stagnant water, which may be why they have an appetite for sewage.


As with any fly infestation, the first place to start is sanitation. Look for breeding sites around slimy drains, backed-up sewers, compost piles, septic tanks or other moist places. A good drain cleaner followed by boiling hot water should take care of any larvae, pupae and adults in and around a drain, but eggs can be protected by a gelatinous film; until you eliminate breeding sites, you’re likely to have a recurring drain fly problem. Your Clark Pest Control technician can help you find any breeding sites, and will treat them to control any drain fly infestation you might be experiencing.

Latin name: fam. Psychodidae: Psychoda phalenoides, P. alternata, P. satchelli, Telmatoscopus albipunctatus, et al.