What Are These Super Tiny Bugs Crawling Up Through My Drain?

Characteristics

• Drain flies, scientifically known as Psychoda alternata, are about 1/6 inch long. Their dark, scaled wings are held over the body when the fly is still, giving it the appearance of a tiny moth. When the bug is crushed, the wings give off a cloud of dust that can be irritating to the lungs of people with asthma. Although these non-biting flies are often considered nothing more than a nuisance, it is theoretically possible that they could transmit disease, especially in cases of large infestations. Because they feed on the gelatinous slime that lines drains, these flies are often found hovering and crawling around sinks. They are also attracted to standing water, such as that found in infrequently used toilet bowls and toilet tanks. The presence of many drain flies in your house is a strong indication of a breeding site.

Life Cycle

• The life cycle of the drain fly lasts 10 to 15 days and begins when eggs are laid in the slime inside drains. The larval form, which is worm-like and 3/8 inch long, feeds on surface films on stagnant water; drain pans under refrigerators are a common site for larva, as are pools of water from leaking pipes. Emerging from the water, the adult flies breed and lay eggs, beginning the cycle again. The life cycle slows down at lower temperatures but continues even when the weather is cold. Drain flies can persist through the winter indoors.

Eliminating Breeding Sites

• To determine if drain flies have chosen a drain for a breeding site, University of Kentucky advises coating a clear plastic cup on the inside with vegetable oil or petroleum jelly. Turn the cup upside down over the drain, where it will catch emerging adults. Using a commercial drain cleaner may be sufficient to remove the organic matter; you can also clean pipes and traps with a stiff, long-handled brush. After cleaning with a brush, flush the drain with boiling water and bleach to loosen and disinfect any remaining slime. However, take extreme care to never pour bleach down a drain after you have used a drain cleaner; this can cause the release of dangerous chlorine gas.

Additional Measures

• To eliminate additional breeding and feeding sites, clean out dirty garbage containers and trash cans, remove any wet lint from under washing machines and empty drain pans under refrigerators. Fly traps and flypaper can help eliminate adult flies that haven't been killed by the sanitation measures. Adult flies can also be sprayed with an insecticide marketed for small flying insects; look for a brand containing pyrethrins. Read the label directions carefully and follow them exactly. Ohio State University Extension warns that you should never pour or spray insecticide into a drain. Because drain flies can breed outdoors and then make their way inside, you should also clean any clogged gutters, soggy areas under air conditioning units and birdbaths. Finally, repair any broken or leaking pipes.