Sewer Flies

Sewer flies ( Psychoda species) are also known as moth flies, filter flies, and drain flies. They are ¼" size and their bodies and wings are covered with grayish, long hair that gives them a moth-like, fuzzy appearance. They hold their pointed wings roof-like above their bodies while they are sitting. They are weak fliers.

Where do you find sewer flies?

Sewer flies breed in areas that are moist and have a lot of organic debris. They can breed in overflow cuts, sinks and tubs, wet lint under the washing machine, sump pump pits, and sewers. Outdoors, they can breed in air conditioners, birdbaths, shallow stagnant pools of water, and standing water. Adult sewer flies can enter homes from the drainpipe openings of kitchen sinks, bathtubs, and toilet sinks and can rest indoors on the walls.

What is the life cycle of sewer flies?

Females lay small, cream colored eggs in small masses (30 -200) in the muck or slimy, gelatinous material that covers the walls and screens of drainpipes. Eggs hatch within 32-48 hrs at room temperature. Their larvae are elongated, flattened, legless, white or pale, with a dark, striped appearance. Larvae have a long thin tube at their posterior end for breathing and a suction cup underneath their bodies that they use to stick to slippery surfaces. There are four stages of the life cycle: eggs (oblong and white); larvae (four stages); pupae (inactive stage from which the adult emerges); and adults. Development from larvae to pupae takes about two to three weeks. Adults live for two to three weeks depending on environmental factors such as temperature and availability of food sources. There are many generations in one breeding season (mostly summer).

What do sewer flies feed on?

Adult sewer flies feed on liquids such as nectars, sugars, and fruit juices. Larvae feed on organic material and bacteria found in the gelatinous material on the walls of drainpipes and sewers chambers.

Do sewer flies transmit diseases?

Adult sewer flies do not bite or sting and do not require blood for egg development. They do not transmit diseases, but they may transfer bacteria from decaying vegetables, fruits, and trash to kitchens. Their decaying bodies can cause allergic reactions in sensitive people.

What can I do in my home to control sewer flies?

Aerosol can kill adult sewer flies, but you must eliminate the larval breeding site to control the sewer fly infestation. To find their breeding site, place a clear plastic disposable cup on the openings of all the drainpipes in your home. The emerging adults will collect in the cup over the infested drainpipes' opening. You must clean the drainpipes in kitchens, bathtubs, toilets, showers and laundry rooms each week to control the sewer flies. Always clean the drainpipes with wooden sticks that have flagged margins and/or a stiff brush to remove the slimy gelatinous material and hair plugs from the drains. Then clean one to two feet of drain using a "snake" (plumber's rod). If you clean all the drains thoroughly, this should suffice. Otherwise, you may also want to use commercially available bacterial digester (Gel) to stop the formation of gelatinous material in the drainpipes.

If the above does not work, consult an exterminator and/or a plumber to assist you in controlling the infestation.

More Resources

Photographs from: UC Statewide IPM project, © 2000 University of California

For more information on sewer flies, call 311 .