Drain Fly

Summary: The drain fly is a little pest that hang out inside drains. It looks like a tiny moth, so it is sometimes called moth fly or drain moth. These bugs love hanging out in stagnant water, so the best way to avoid them is to eliminate standing water and scrub off the slick scum from the inside of drains.

The drain fly goes by many names including filter fly, sewer fly, drain fly and drain moth. 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.

credits: Steve Jacobs, PSU Entomology

You are most likely to experience an infestation of drain flies after you have been away from your home for awhile like on a vacation. These pests are often found in stagnant water. So once the drains in your home have running water flowing through them again, you can eliminate any young drain flies. Adult drain flies can escape the wrath of the drain, though. They can survive at cold and hot temperatures, so turning your water on at different temperatures will not eliminate adult drain flies from your drain.

Places that drain flies can be readily found are in moist manure, drain traps, septic tanks, garbage cans, dung, storm drains, damp leaves, inside toilet bowls that are not regularly used, in any type of drain in a garage or basement, and anywhere else that has stagnant water.

Larvae of drain flies are found in bird feeders, moss, thick mulch, or under plants or air conditioners. They feed on decaying animals and plants they find outside; indoors, they eat decaying food in drains. So if you do not clean your drain out regularly, you are practically inviting these pests in as roommates. When you see those black like worm-like larvae you know you've got a drain fly infestation.

Immature drain flies are extremely hard to identify because of their tiny size.

Fly breeding location

However, you can try a simple trick to determine if drain flies are camping out in your home. Take a small plastic cup and spread a layer of petroleum jelly or vegetable oil on it. Set the cup very close to a drainpipe. Wait a couple of days and check the cup. Look closely for any larvae. They are gray with dark bands across their backs. This technique will help you not only find where the drain flies are living, but it will also help you catch them because they will get stuck in the sticky film.

Another way to find out if you have drain flies is to set some fly tape over the opening in your sink, sticky side down. Wait about 24 hours. If you see tiny flies on the tape, you know you have just been paid a visit by drain flies.

Tips to Avoid Drain Fly Infestation:

• Keep your gutters unclogged. Drain flies love gutters full of water for them to live in.
• Check your air conditioning unit's drain every week in the summer. Though it may seem like a hassle, it will prove to be beneficial because drain flies can reproduce quickly.
• Make sure to keep your windows and doors closed in the summertime.
• Buy a fine weave fiberglass window screen for your windows and patio. The small holes in a common window screen are wide enough to allow drain flies into your home. The smaller the holes, the less chances you have of tiny pests flying in.

Tips to Eliminate Drain Flies:

• The most important task in getting rid of a drain fly infestation is to eliminate their breeding site. If you can remove the stagnant water the larvae grow in, they will have nowhere to reproduce.
• Spray your drains or rooms where adult drain flies are found with an aerosol insecticide spray labeled for flies. Sprays used on houseflies will work on drain flies.
• Get rid of any decaying food you have in your home that the flies can feed on. Clean out any areas that drain flies are attracted to, and definitely clean out your drains thoroughly.
• If found in your bathroom or another room with tile, grout your tiles. This will help remove any moisture that has accumulated.
• Check for wet lint underneath your washing machine and get rid of it.
• Get rid of the gunk building up in your drain. Drain fly larvae love to eat this stuff. Do not pour bleach down the drain. Bleach kills bateria. It is not an insecticide. There are products like DF 5000 Drain Cleaner, but it is just as easy to use a toilet brush to scrub out the drain. Really tough cleaning jobs may require some Drano to really clean it out.