I've been battling some relatively slow-moving flying pests and their larvae. Based on my Internet research I'm 90% certain that these are "moth flies".

They are found mostly on the ceiling or on the walls near the ceiling. When they are in a resting state (or when they are larvae) they don't see me coming and they are easy to capture with a napkin. When flying they move a bit slower than flies so I can usually catch them with moderate effort.

The problems I'm having are:

  1. No matter how many I capture or kill, they keep coming back within a couple of hours - I've currently killed an estimated 200 - 300 of them over the course of a week
  2. I can't pinpoint their origin
  3. Fly paper and an indoor UV electric solution perform poorly - I got maybe 10 that way
  4. I can't use chemical sprays or poisons, because I have a young puppy in the house and I'm not willing to risk it

The Internet led me to believe they probably came from drain pipes, so I bought an insecticide made specifically for drains. Not only did it do nothing, when I went to clean and inspect the sink pipes I somehow created a leak. On top of that, I tried to further clean the sink pipe and make the slow drain fast by buying a high pressure air gun made for that, which somehow made the drain pipes totally clogged (I digress - the point is that this option won't work for me). I don't actually see any evidence that they came from the drains at all.

Any thoughts on how to safely eliminate them and/or where else their source might be? I suppose if I found where they keep coming from I could kill their nest or egg sacs or whatever, but they seem to appear from thin air.

  • 1
    You can kill them instantly with a safe homemade spray: 4 parts water, 1 part Murphy's Oil Soap. Drops those suckers right out of the sky, dead before they hit the ground. You won't find a nest or egg sacs, they come from maggots, which live in moist out of the way places rich with food.
    – dandavis
    Sep 25, 2020 at 18:57
  • @dandavis Thanks. Are maggots the same thing as the larvae? Maybe originally they grew in some garbage bags I was keeping in the sun room waiting for trash day, but those are gone now and I don't see where they keep coming from. The rest of the food in my house is sealed up in the refrigerator. Anyway, will this eventually eliminate all of them? I'm able to kill them 1 by 1 already with napkins and fly swatters, but they just seem to keep coming and coming.
    – Hack-R
    Sep 25, 2020 at 19:09
  • They could be from a dead animal in the wall, still around from the trash, or the fatberg in your drain. If you cannot locate the source, you will have to deal with them until the nutrient source is depleted, usually a week or two. Fix the drain, then dump some bleach down it.
    – dandavis
    Sep 25, 2020 at 19:36

3 Answers 3


Really if it is like that you can do two things:

  1. As Dandavis suggested - water+murphy's oil takes care of it fast. It works, I have used it multiple times.

  2. You need to do a thorough cleaning. This is emptying under the sink, moving oven out and cleaning under, same with fridge, trash can (I had an insert in my last trash can and in between the insert and the bottom was food and it was a nightmare - so perfectly clean kitchen and one clump of food hidden), take out all bottom drawers and make sure nothing is under them, all cabinets, pantry, and on top of cabinets.

There is always a chance that you could have a dead animal in the wall but it usually isn't the case.


Could be pantry moths. They often show up in dry goods (e.g. rice, oatmeal) purchased from outside.

My solution was

  1. Place all food in hard sided sealed containers.
  2. Clean all shelving.
  3. Clean all ceilings and walls.
  4. Deploy pantry moth traps.
  5. Wait a couple of weeks, making sure that all starchy items are in jars/hard sided containers.
  6. Inspect jars and hard sided containers for moths -- they sometimes lay eggs on the insides of the jar lips.

It takes months to get rid of them.

  • Very helpful. Could've been an old dog food bag. I've thrown it out now.
    – Hack-R
    Sep 25, 2020 at 21:45

I have no doubt these pests came from the sewer. (I've heard them called sewer flies, and I see them all the time when I pop sewer manhole lids for work) They can't swim, so my first guess is that the trap under your sink isn't holding enough water to block gas exchange from the sewer, so they might be flying up and through the trap. My second guess is there's a break in the vent stack somewhere that allows them entry.

You mention having a slow drain, and that you "somehow created a leak" by working on it. That leak could easily be draining the water from the trap so I would start there.

Edit: Here's a good youtube video on how a p trap works. It also mentions that if the vent stack is clogged the water can be sucked out of the trap, which is something I didn't consider!


  • Thanks much, I will check it out
    – Hack-R
    Sep 28, 2020 at 0:02

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