Small Flies Coming From the Drains? What to Check First
Small flies coming out of drains are usually drain flies, breeding in the film of gunk inside the pipe. Fruit flies and phorid flies cause the same complaint. The fastest way to narrow it down: press clear tape sticky side down over the drain overnight and see what sticks to it.
What it usually is
| What you see | Most likely | How to tell |
|---|---|---|
| Fuzzy gray flies sitting still on the wall or tile near a sink or shower drain | Drain flies | They look furry, almost like tiny moths, and fly in short clumsy hops instead of buzzing around the room. |
| Small tan flies hovering over the sink, the trash can, or the fruit bowl | Fruit flies | They have reddish eyes and gather around anything sweet or fermenting, not just the drain itself. |
| Dark flies about fruit fly size that dart away on foot when you reach for them | Phorid flies | They run across the counter in quick zigzags before taking off, and a steady stream from a floor drain can point to a leak or break in the line below. |
| Slender black flies drifting near windows and houseplants close to the sink | Fungus gnats | They come from damp potting soil, so you'll see them lift off when you water or bump a nearby plant. |
Check these in the next 10 minutes
- Press a piece of clear tape sticky side down over the drain opening tonight and check it in the morning. Flies stuck underneath means they're breeding inside that pipe.
- Shine your phone flashlight under the sink and around the base of the toilet, looking for standing water or a slow leak.
- Check the trash can, recycling bin, and any fruit on the counter for anything overripe or leaking.
- Look at the soil of houseplants near the sink. Tiny flies lifting off damp soil points away from the drain.
- Snap a photo of one resting on a wall and run it through the free identifier at pestpin.com/identify to narrow down what you have.
Narrow it down with the free identifier
Answer a few questions about what you are seeing and we will narrow the likely pest, with an honest confidence level. It is a starting point, not a guaranteed identification.
What kind of place or property is affected?
This helps us point you to the right kind of professional, not just guess a bug name.
When to bring in a licensed company
If you've scrubbed the drain, cleared out ripe fruit and trash, and flies are still showing up two weeks later, they're probably breeding somewhere you can't reach. A steady stream of flies from a floor drain or a spot where a pipe runs under the slab can mean a break in the line, and finding that takes a plumber or a pest control pro with the right tools.
Common questions
Why are small flies coming out of my drain?
A slimy film builds up inside drain pipes, especially ones that don't get used much, and drain flies lay their eggs in it. The larvae feed on that film, then the adults crawl up and out of the drain. That's why they keep showing up after you swat the ones you see: new adults keep emerging until the buildup inside the pipe is gone.
Does pouring bleach down the drain kill drain flies?
Usually not. Bleach runs straight past the film where the eggs and larvae live without soaking in, so new flies keep coming. Scrubbing inside the pipe with a stiff brush and using a drain gel made for organic buildup works better, because it removes the material they breed in. If you use any product, follow the label exactly.
Are drain flies harmful?
Drain flies don't bite, and in most homes they're a nuisance that points to buildup in a pipe rather than a danger. The bigger concern is what a heavy, constant stream of them can mean: flies pouring out of a floor drain or a rarely used bathroom sometimes trace back to a plumbing problem like a leak or a broken line, and that's worth finding early.