How to identify it
Also called moth fly, sewer gnat. Work down these in order — the first one is usually enough on its own.
- Densely hairy body and wings, giving a fuzzy, moth-like look
- Wings held roof-like over the body at rest, forming a heart shape from above
- Weak fluttering flight — it hops more than it flies
- Beaded antennae
What it gets mistaken for
Most people arrive at a pest name by ruling things out. These are the ones that genuinely look similar, and the detail that separates them.
Where you will find it
- On walls near sinks, showers and floor drains
- Inside seldom-used drains, especially in guest bathrooms
- Around condensate lines, sump pits and grease traps
- Anywhere a film of organic sludge stays permanently wet
Signs it is already there
You will nearly always see the evidence before you see the pest itself.
- Small fuzzy flies sitting motionless on a bathroom wall
- Numbers rising after a rarely used drain is run
- A sticky film inside the drain when you actually check it
Low. Nuisance rather than hazard.
Why it is harder to deal with than it looks
They breed in the gelatinous film lining the inside of the pipe, not in the standing water. Bleach and boiling water run straight past that film and change nothing, which is why the problem comes back within days.
What actually works
Scrub the inside of the pipe mechanically with a stiff drain brush, then use an enzyme or bacterial drain cleaner that digests the film. To find which drain is the source, tape clear tape sticky-side-down over each suspect drain overnight and see which one catches flies.
Common questions
How do I tell a drain fly from a house fly?
House flies are several times larger, smooth and grey, with four dark stripes on the thorax.
How do I tell a drain fly from a mosquito?
Mosquitoes have long legs, narrow wings and a piercing mouthpart, and never look furry.
Where are drain fly usually found in a home?s
On walls near sinks, showers and floor drains Inside seldom-used drains, especially in guest bathrooms Around condensate lines, sump pits and grease traps.
Is a drain fly dangerous?
They do not bite and are not a disease risk in a household. They are an indicator that a drain needs cleaning.
Identification guidance only. Under Texas law, applying pest control treatments for hire requires a licence from the Texas Department of Agriculture. This page describes what a pest looks like — it is not a diagnosis of your property or a treatment recommendation for it.