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Drain Fly

Summary: The drain fly hangs 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.

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 like PT 565 XLO. 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.  Drain Gel will remove the "slime" where the flies breed. 

Both products mentioned are sold on this website. Just click on the red, highlighted word to see the product(s).

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.

If you have drain flies breeding under the floor slab you may have to open the slab and have all the contaminated soil removed. These flies live in the algae and mold that grows in wet environments. Do not try to spray more liquid pesticides into cracks in the slab. It will only make matters worse. The moisture problem must be located and fixed. Call a plumber, not an exterminator.

Ask Rick A Question


Suzi M
30 Aug 2011, 20:06
I just move into a home about 2 months ago. And I like to take baths on a regular bases and I had noticed this little i mean little black bugs that had almost clear wings on them in the tub with me it would be maybe one or to. but recently they are all over my tub and i have to clean my tub daily just to take a shower. When i find them they are near my drain mostly and they are dead. i have seen them near my sink in my bathroom but not many does anyone know what these are? and how do i get rid of them?
Ask the Exterminator
31 Aug 2011, 12:36
Identification is the first step. I cannot ID your insects from your description, so collect a few in a jar and take them to your local county extension agent for a free ID. Once you know exactly what you have you will quickly be able to find information about where they nest and how to control the problem.
08 Sep 2011, 00:51
Do these flies die out in the winter?
Ask the Exterminator
08 Sep 2011, 16:40
Their populations decrease, but they do not die out in the winter.
22 Oct 2011, 17:08
I recently found a large amount of black worms (tiny, maybe 1/4" long or less) swimming around in the water under my dish drainer. The dish drainer is sealed around the edges where it meets the water catcher portion, but there are little holes in the top (so water can drip down) so a fly could have potentially gone down there to lay eggs. My question is: I have not seen these anywhere in our house, near any drains or toilets, only in this particular drainer (used for my kids bottles!) which is 2 feet from the sink drain. Can I be pretty certain these are drain fly worms? I see some fruit flies in our home but nothing else flying around. How did they get into the dish drainer? Are they in our water, the eggs, and then they hatch after sitting in the water draining bin? Looking at the worms they are blackish brown and when I shake the jar I put them in there is some shedding of a clear skin with black stripes. Should I just treat all the drains and assume its not in our water supply? Or could it be in our tap water?
Ask the Exterminator
23 Oct 2011, 10:52
Drain flies develop in the slime that collects along the inside of the drain pipes. Clean the drain with a round brush and dishwashing detergent and rinse with water and you will be rid of the fly breeding problem.
01 Feb 2012, 01:09
I have drain flies in my house. We have a furnace room in the basement that has an ejector pit that is sealed and a drain right next to it. I have seen them near the drain. Ive tried bleach in the drain with no luck. I tried a hot shot pest strip that has worked in the room. However they return when I take it out. My question is, are they in the ejector pit? We have s bathroom that ties into it. I would rather not unseal it and clean it unless I have too, or do you think just cleaning the drain will work?
Ask the Exterminator
18 Feb 2012, 13:02
Drain flies, also known as drain moths, usually are associated with drains that have gone dry. My guess is that you have Phorid flies. To be sure, collect a couple of flies and get them properly identified before you try control measures.
02 Jun 2012, 19:01
We recently have been seeing these drain flies in our Masterbath. The walls of our shower are marble, and the floor is tile. I have noticed the worms are more around the crease at the bottom of shower door. I have cleaned and scrubbed, and made myself sick (respitory). The drain in our shower keeps getting a clog of somekind it is white and very hard to clean, I actually have to scrape it off tiles, and inside drain. I have read that it is best to use a product like df 5000 drain gel. But it is not easy to find. What is your opinion on how to handle issues?
Ask the Exterminator
03 Jun 2012, 09:03
The clogging drain problem needs to be resolved. The inside of the drain is often a breeding area for drain flies.
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