Most people are familiar with pantry pests and moths, but few have ever heard of drain flies unless they have had them in the house. Most people discover them around the bathroom or kitchen sink and mistake them for gnats or moths because of their hairy appearance. They do not cause diseases, but they can spread dirt and bacteria from one place in the house to another. The adults are not strong fliers so infestations usually occur in the same area where the adults are reproducing. While these pests are not found in every house, they can be easily eliminated from your house by taking a few simple steps.
Drain flies go by several names-filter flies, moth flies and sewage gnats. They are in the family Psychodidae and are not a moth or gnat, but a fly. The adults look similar to moths in the way they hold their wings at rest, are attracted to lights in the evening, and have a hairy appearance. The adults are 3-4 mm in length and live two weeks after hatching. Drain flies vary in color from black to brown to yellow. The larvae are found in drain traps or moist places with a lot of organic matter and are pale yellow to white in color, about 4-7 mm in length. The larvae are extremely resistant to heat, cold and low oxygen environments, so do not expect that when the seasons change, the population will disappear. It can take one to three weeks for the drain flies to complete their life cycle, so when treating an area, take in consideration that you may have a second generation hatch from their pupae if you simply spray the adults with an aerosol spray.
If you think you have an infestation, but are not sure where the adults are laying eggs, tape a piece of plastic over the suspect drains for at least 12 hours. If there is an infestation in the drain, you will notice adult flies on the drain-side of the plastic. If the flies are not in the drain, look for other suspect areas around the house. These include houseplant saucers, storm drains, and decaying plant matter. Simply by cleaning up excess water or removing the plant material from these areas, you can prevent the flies from producing more generations. If your infestation is coming from the drain, take out the drain trap and scrub with a brush to remove the sludge that has accumulated and/or pour a drain cleaner at the recommended rate down the drain to clean the pipes and the trap. At this point, most populations will be eradicated. However, if you continue to see the flies after treating the pipes or doing clean up around your houseplants, you may need to hire a plumber to check for leaks in the pipes either behind the walls or in the ground outside. If you are not sure if the bugs you have are drain flies, or have other pest questions, call us at the UGA Cobb County Extension Office at 770-528-4070 or e-mail us at uge1067@uga.edu and we will do our best to assist you.
-Rachel Prakash
Horticulture Program Assistant
Reference:
http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls30drainflies.pdf
http://hgic.clemson.edu/factsheets/HGIC2405.htm
http://www.entomology.cornell.edu/Extension/DiagnosticLab/IDLFS/DrainFlies/DrainFlies.html
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