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Old 09-11-2008, 02:41 PM   #1
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Drain fly infestation

I've been fighting a persistent, severe infestation of drain flies in my home for many months. I'm at my wits end and looking for help in figuring out exactly where they are hatching so I can eliminate them. Here's what I know:
  • I am averaging 50-100 flies a day that spread throughout my small home but definitely originate in my one small bathroom. I know this because if I close the bathroom door they all collect there and not elsewhere in the home. They migrate towards lights, windows, and bright surfaces.
  • I keep both drains (sink and tub) sealed off at all times when not in use but I get them anyway, so they are not coming from the drains. I have also repeatedly cleaned the toilet tank and bowl including under the rim.
  • The septic tank is just outside of the bathroom, and I have sealed off all possible channels I know of for ways they might get in the home from the septic apart from the drains. I have sealed the open space beneath the drain plug lever, the drain spout, and checked for any wall cracks that might lead to the space behind the wall which in turn might allow access from the septic area.
  • I keep the room clean, and are no known loose tiles or other areas where mold or slime might form and allow them to breed..

If the drain flies are breeding in the bathroom, would I be seeing larvae somewhere? If so, how big are they? Any other signs, symptoms, or techniques involved with identifying breeding areas?

These things are unbelievable. At times I can shut the bathroom door, kill all that are there with flying insect killer, and stand there motionless and within a few minutes more appear, seemingly out of thin air. This is a small bathroom, and Iíve stared and stared at all wall and floor surfaces and see no sign of larvae or where they come from.

Any advice or help appreciated!


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Old 09-11-2008, 08:53 PM   #2
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I can only offer a guess. The pipe connecting the toilet to the main stack must have a small leak. But not enough to show signs. Do you have a cabinet below the sink? I think the flies are making their way through the wall using the access holes where plumbing enters and leaves. Another thought is that you might have animals finding a way inside the house but get trapped and then die in the ceiling or walls. Years ago, I had a bunch of flies on the inside of my basement window screen. I knew right away that they did not enter through any door or window. So there must have been a bird that got in and it entered by the roof area and must have found a way into the basement wall. The wall had a opening at the ceiling area where the animal got stuck above the opening and died.
Start with the sink cabinet and check for openings where they might possibly enter where the pipes are. I think in all homes, there will be enough space arounf these pipes for flies to enter. Place one of those sticky fly traps near the opening and close the cabinet door and check it later.


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Old 09-12-2008, 09:15 AM   #3
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Closing the drains only stops water flow from the sink or tub into the drain. The other path where the little buggers could be doing the happy dance is in the over flow; most sinks have them and the tub definitely does. It could be that there's a bunch of gunk built up in the over flow i.e. soap scum, hair dirt and grunge, that's supporting their life style. Try plugging the over flow spout (blue painters tape) with the drain closed to see if it slows them down. If it does, you know where to start cleaning...
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Old 09-12-2008, 04:55 PM   #4
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x2 on the overflow. I put duct tape on one I had in my last apartment. Took care of the problem. You have to get rid of the gunk.
"Aw! Why does everything that only happens to stupid people happens to me?" - Homer J. Simpson
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Old 09-12-2008, 10:52 PM   #5
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It depends on what you are calling drain flies

I have seen two different types routinely called drain flies

If they are the gnat looking flies then your problem is most probably coming from the drains
Usually they develop in unused drains
If this is a bath that nobody uses the fix could be as easy as running hot water down the drain for about ten minutes a couple of times a month

If it is a frequently used bath then it is probably the over flows

There is a product called Drain Gel that is a biodegradable liquid that you squirt into the effected areas

Drain flies will also live in potted plants if you have any in there or any wet organic matter

If they look like miniature house flies with their wings sticking out to the side they are moth flies and usually are a sign of a pipe leak or standing water under the drain pan or in the wall
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Old 10-03-2008, 08:52 AM   #6
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Problem resolved!

Thanks to all for the replies. I am happy to say I finally found the source of the drain fly infestation, and it was a surprise as it had nothing to do with drains or other areas you might expect. I'm adding this post in the hopes that someone else with a perplexing infestation like mine will find it helpful.

There is a double hung aluminum window on the long wall in my shower. In between the two panes there is installed a small line of felt to provide a weather seal. It appears that my severe infestation was all stemming from eggs being laid in that little strip of felt.

Once I flipped the window open and soaked that area I started getting dozens of dead flies appearing there by the hour. I had to keep up the soaking with insecticide for about a week, and now I am free of the damn things.

So, the key to drain flies is to keep searching until you find the moist, soft, damp area they breed in.
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Old 10-05-2008, 05:42 PM   #7
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Consistantly (bi-weekly) treating your drains with Drain Gel and an IGR like Archer will eliminate the conducive conditions that allow Drain flies to multiply.

Last edited by AtlanticWBConst.; 10-05-2008 at 07:47 PM. Reason: SITE RULES VIOLATION: Advertising Link Removed From Signature
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Old 04-10-2009, 07:48 PM   #8
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How did you find the breeding source?


I have been trying to find the breeding source of these flies for over a month. These have been driving me crazy and it is so difficult to figure out which area they are originating in. I have tried the drain cleaners and put clear tape over them and there is no way they are coming up from there. My house is so clean and spotless.

How did you know to check such an obscure place for the breeding site? What did the breeding site look like so I can start to search in not so obvious places?

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Old 10-06-2009, 12:12 AM   #9
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I think it's a drain Fly

We had a pest control come in and fog our bathrooms and hallway. We are extremely clean and have cleaned our bathrooms numerous times. I think it's a drain fly based upon everything we have seen online but not sure. I recently cleaned the 2 bathrooms spotless from ceiling to floor just to see what would happen again (after Fogging). I cleaned during the day waiting for night fall (since this is when they seem to be most active, very active) and then all of the sudden 1 then another and I killed each one after another. Finally I was fed up and stopped. I put fly catchers over my drain and sealed the other drain and pulled the stoppers on my sinks. They were still coming out of nowhere. Anyhow, I stopped killing each one by one last night just to find there were dozens more this morning. I have looked everywhere and am thinking of fogging again and am not sure what else to do!! In fact, I just sprayed our window's like the other POSTER did and we'll see what happens.
Anybody have any suggestions that can help this upset family???

Thank you
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Old 11-23-2009, 07:37 PM   #10
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start at 1:20
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Old 12-30-2009, 10:24 PM   #11
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I'm glad Marksto found his solution. Gnats or flies can breed in the darndest places. For najlex1 I'd say the drain gel is great for drain flies but there is one such critter that can come from way deeper in the drains or up through teeny cracks in the foundation. The Sphaerocerid flies can last a long time and are almost immune to the drain gel. Try DF5000 in suspected drains according to the label and when the problem gets better you can go to the drain gel. If it is outside the pipes and say from a crack you may need a moisture meter or a real pro who knows about this fly to get you help. They can be 20 times more maddening. But whatever the case be persistant because unless the moisture dries up the source will always be there. Search for the DF5000 on the net-it's about $17.00
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Old 05-20-2010, 10:34 PM   #12
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Pest control

Hi guys. This is my first post. I read your post about drain fly infestations and found some helpful suggestions, but I have this problem withlittle black flies with wings (that stick out on the sides )tthat smear when I catch them on tissue. I have also noticed little black spots on the floor to my masterbath, and when I wipe them up, they smear too. They don't seem to be insects on the floor, just the black spots lined against the wall and at the bottomof the molding. I have even seen little dark brown or black spots (they look like tiny round droppings) and some look like eggs of some sort also on the sink in my kitchen and bathroom. They have been therefora long time because I did not know what todo about them. I bought the house new, and I had, from the beginning, problems with the plumbing, leakage in the basement, mold on the windows, etc. I also have seen these tiny little black flies when I comb my hair. they will fall into the sink and sort of hop, and I have a crawling sensation on my scalp and when I comb my hair, these little black and brown dots some smaller than a pin head, fall into the sink. I've seen them in the sink, in the tub drains. This is torture! I cannot invite anyone to my home because of this problem. I've tried everything to get rid of this unsanitary problem. I've sprayed with Archer, with permetrin, with igr until I've made myself sick. Does anything that I've said sound familiar to you? Do you think these things are moth flies, drain flies, or what?How can I get rid of them? Please, please help. They are driving me crazy!!!
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Old 05-20-2010, 11:14 PM   #13
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Wow that doesn't sound good. It doesn't ring any bell with me I'm sorry to say.
The moisture sounds like the contributing factor though. Can you run a dehumidifier? If you can dry the place up and fix the plumbing it may solve your problem. For the drains put some bleach down them and have the duct work examined and possibly cleaned. I don't think spraying is going to help in this case so I'd lay off the heavy application.

Sorry I couldn't be of more help.
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Old 05-21-2010, 06:32 AM   #14
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honeywhite, get a good magnifying glass and give the critters a good look.
Google bed bugs, lice & any other tiny bugs that come to mind.

good luck I hope this becomes an easy problem to solve.
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Old 04-12-2011, 08:42 PM   #15
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help please with drain fly infestation

Hello, and thanks for reading my post.

We live on the 30th floor of a New York City apartment. I have a drain fly infestation, and according to my Superintendant I am the only tenant that has complained.

The flies seem to be based in my master bathroom, but we can not locate the source. Also even more than my bathroom the flies congregate around the windows all over my apartment, in all three bedrooms and the living room by the windows. Every day there are tons of them by the windows, dead and alive.

I have taped over the drains and found nothing. I have poured bleach down the drains many times. The exterminator has poured foam down the drains. I have left cups of oil as someone suggested around the apartment to try to locate the source to no avail. I have had the a/c units checked. The plumber is coming tomorrow to snake the drains. I do not know what to do! I have no idea where they are coming from. This is driving me crazy, we must kill about 50 a day. They are everywhere!

Does anyone have any suggestions at all? Have you heard of photo imaging to find moisture behind the walls? How does a moisture meter work? Will it detect moisture behind the tile in my bathroom? I am not in the business, I am a housewife but I am handy and I am willing to spend money to get rid of these f***kers. I am going bananas here and I am obsessed with getting rid of them.

Thank you.



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