How to Get Rid of Drain Flies
If you're seeing small, fuzzy, moth-like flies hovering around your bathroom sink, shower drain, or kitchen, you're probably dealing with drain flies. They're also called moth flies, sewer flies, or filter flies, and homeowners frequently confuse them with the similar-looking phorid fly. Whatever you call them, the fix is the same: find where they're breeding and remove it.
What Are Drain Flies?
Drain flies are small flies in the family Psychodidae, usually about an eighth of an inch long, with a fuzzy, tan to gray body and wings that fold flat like a tiny moth's when at rest. They're weak fliers, so you'll typically find them resting on walls or tile near a drain rather than buzzing actively around a room.
Unlike mosquitoes or biting flies, drain flies don't bite and aren't known to spread disease to people. The problem they cause is presence and persistence: once a drain is breeding them, new adults keep appearing day after day until the breeding site is addressed.
Phorid Flies vs. Drain Flies: What's the Difference?
Phorid flies (family Phoridae) are a separate species, sometimes called humpbacked flies for the way their thorax arches, or scuttle flies for their habit of running erratically across a surface instead of flying away. They're a similar size and color to drain flies, which is why the two get mixed up so often.
The practical difference: drain flies breed almost exclusively in the organic film that lines older or infrequently used drains, while phorid flies will breed in a wider range of decaying organic matter, including drains, garbage disposals, and rotting produce. If your flies are showing up specifically near a drain and you see fuzzy, moth-shaped wings held flat, drain flies are the more likely culprit. Either way, the fix below applies, since both breed in the same kind of buildup.
Where Sewer Flies Actually Come From
Drain flies don't come up from the municipal sewer system, despite the nickname. They breed inside your own plumbing, in the layer of organic buildup, sometimes called biofilm, that forms on the inside walls of a drain pipe over time. That layer is made up of soap scum, hair, grease, and food residue. In a drain that isn't used often, a guest bathroom, a floor drain, a rarely used shower, it can sit undisturbed for weeks, giving flies exactly what they need to lay eggs and thrive.
Drain Fly Larvae: What They Feed On
Drain fly larvae live inside that same organic film and feed directly on it, along with the bacteria and organic matter growing there. They don't feed on anything else in your home, and they don't travel far from the drain that produced them. That's useful to know: if you're seeing drain flies concentrated in one spot, the breeding site is almost always that exact drain, not somewhere else in the house.
The larvae mature within the film over roughly one to two weeks before emerging as adults. Adults are short-lived, but as long as the film is intact, new eggs keep replacing them, which is why an infestation can look constant even though individual flies don't live long.
How to Get Rid of Drain Flies
Because drain flies breed in organic buildup, not standing water, killing the adults you can see does almost nothing on its own. New flies keep emerging from the film until the film itself is gone. A few steps make the difference:
- Find the drain. Check every drain in the affected room, including floor drains and rarely used showers, since drain flies favor drains with slow flow or infrequent use.
- Clear visible debris. A drain brush or a bent wire can pull out hair and larger buildup near the opening, but it won't reach the film coating the pipe walls further down.
- Treat the buildup those tools can't reach. This is where an enzyme-based drain treatment matters. It travels past the visible opening to work on the film lining the pipe.
- Repeat on a schedule. A single treatment breaks the current cycle. Regular treatment keeps the film from re-forming, which keeps flies from coming back.
Do Drain Fly Killer Sprays Work?
Aerosol drain fly killer products and foggers are built to kill adult flies on contact, and they do that part effectively. What they don't do is reach the organic film where the next generation is developing. Spray the visible flies today, and if the film underneath is untouched, you'll likely see new adults again within a week or two, because the breeding site was never addressed.
That's the core issue with any adult-only approach: it treats the flies you can see and leaves the source alone.
Enzyme Cleaner for Drain Flies: How It Works
Earthworm® Drain Cleaner does not kill drain flies, and we want to be direct about that: it isn't labeled or sold as an insecticide. What it does is remove what the flies and their larvae depend on. The formula introduces live, enzyme-producing bacteria that travel down into the drain and colonize the pipe walls, where they continuously digest the organic material, the grease, hair, soap scum, and food residue, that makes up the biofilm. As that film breaks down, the flies lose both their food source and the surface they lay eggs in. Without a film to breed in, the cycle breaks on its own.
It's a slower approach than a spray, and it won't clear a room of flies in an afternoon. But it addresses the reason the flies are there in the first place, which is why it holds up over time in a way that killing visible adults doesn't.
How to Use It in a Drain Fly Situation
Pour Earthworm® Drain Cleaner directly into the affected drain and let it sit, ideally overnight, so the bacteria have time to establish before water runs through again. For an active drain fly problem, treat weekly for the first two to three weeks to work through the existing buildup, then shift to a monthly maintenance dose to keep the film from re-forming. If the same drain is also running slow, see our guide to fixing a slow drain for the full dosing schedule.
When to Call a Plumber
Most drain fly problems resolve with consistent treatment of the organic buildup. If flies keep appearing after several weeks of regular treatment, or if you're also noticing sewage odors, gurgling, or standing water, there may be a cracked pipe, a dry P-trap, or another plumbing issue feeding the problem alongside, or instead of, buildup. That's worth a plumber's look rather than more product.
Ready to Get Ahead of It?
Earthworm® Drain Cleaner uses live enzymes to digest the buildup drain flies need to survive, without harsh chemicals, and it's safe for septic systems.
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