Drain flies (or moth flies) are small, dark, fuzzy, moth-like insects. They are weak fliers, typically flying only a few feet at a time. They are often found clinging to the walls of bathrooms, kitchens, or in the basement. During the day, adult flies rest on walls or on the sides of tubs and shower stalls. They become more active at night, hovering over drains, sinks and other breeding areas.
It is a teeny little bug that is commonly seen around drainpipe openings. It measures no longer that 1/5 of an inch, so it can be very hard to spot at times. It has hairy, dark wings that make it resemble a miniature moth. Fortunately, drain flies do not bite. Unfortunately, they multiply like crazy, fly out of drains and hang out on a walls and ceilings. It is not a good flier, so if you notice drain flies in a room, you will most likely find its breeding source in that room.
Drain flies lay eggs in a mass of 30 to 100. These eggs hatch in less than 48 hours. The larvae and pupae of the drain fly live in the thin film found in drains, septic tank field lines or filter stones. The larvae feed on sediment, decaying vegetation and microscopic plants and animals. The larval stage lasts from 9 to 15 days and the pupal stage lasts from 20 to 40 hours. The newly emerged adult fly is sexually mature on emergence and copulates within the first few hours of its life.
The most effective method to correct (or to prevent) drain fly problems is to clean toilets, drainpipes and traps to eliminate any gelatinous rotting, organic matter, thereby eliminating the larval food source. Many of the commercially-available drain and toilet bowl cleaners can be used for this purpose. Many of these cleaners are biodegradable and pose less of a hazard to the environment. If you have a septic system, read the product labels carefully to make sure that the product is compatible with the system (i.e., will not disrupt the microbial action in the septic tank). Routine cleaning of floor and sink drains is important particularly in commercial establishments.
Indoors, aerosol sprays of pyrethrins (or other "flying insect" sprays) will kill adult drain flies, giving temporary control, but they are not a real fix for the problem. If the drain flies are coming from an outdoor source, exterior applications of any common residual sprays for flies can be made around windows for temporary relief until the source of the infestation can be found and eliminated.
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