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Those tiny moth-like flies breed in the gunk inside your drains. Here is how to find the source, clear it, and keep them gone.
Call (888) 217-5859Small, fuzzy, moth-like flies hovering around a sink or shower drain are drain flies, and they are telling you something about the drain itself. They are harmless, but they breed in the organic film that builds up inside a dirty or slow drain, so the way to get rid of them for good is to clean out what they are breeding in. Spraying the adults does nothing if the gunk they lay eggs in is still there. Here is how to find the source and clear it.
Drain flies - also called moth flies, sewer flies, or sink gnats - are tiny gray or tan insects with fuzzy, moth-like wings. Unlike fruit flies, which swarm around food and ripe fruit, drain flies stay near drains and damp spots and rest on the wall nearby. They don't bite or carry disease into your home, but a cluster of them is a reliable sign that a drain somewhere has a layer of buildup inside it.
Drain flies lay their eggs in the slimy film of hair, grease, soap, and food residue that coats the inside of a pipe - the same organic buildup behind slow drains and odor. Any drain that is used rarely, draining slowly, or simply overdue for a cleaning becomes a breeding site. A guest bathroom, a basement floor drain, a utility sink, or a kitchen drain with grease buildup are the usual sources, and standing water in a little-used trap is a classic spot.
Before you clean, find the source. Dry the area around each suspect drain, then tape a clear cup or a strip of tape loosely over the drain opening overnight, leaving a small gap for air. Adult flies emerging from that drain get stuck on the tape. The drain that catches flies is the one to clean - and it is often not the spot where you see the most flies resting.
Once you know the drain, clear what they breed in:
Two common approaches fall short. Spraying or swatting the adult flies feels productive but ignores the eggs and larvae in the drain, so a new batch hatches within days. And pouring bleach down the drain mostly runs straight through without scrubbing the film off the pipe wall, so it rarely reaches the eggs clinging to the sides. Physical cleaning is what actually ends the problem. The biofilm behind drain flies is the same buildup behind odor, covered in why does my drain smell.
If flies keep returning no matter how often you clean the drain you can reach, the breeding buildup is deeper in the line, in a spot a brush can't touch, or in the main sewer. A heavy layer of grease and sludge coating a pipe is exactly what hydro jetting scours off in a way home cleaning can't, and a drain that stays slow and dirty despite your efforts is worth clogged drain removal to find out why. Persistent flies from a lower drain, paired with slow drains or odor, can point to sludge in the sewer line or a break letting waste sit - the kind of thing a camera inspection confirms, as in signs your main sewer line is clogged.
Keeping drains clean and flowing is the whole prevention strategy, since drain flies can't breed without that film to lay eggs in. Clean kitchen and bathroom drains regularly, keep grease out of the sink, run water through little-used drains, and use a drain strainer - the same habits in how to prevent drain clogs. In older South Suburb homes around Richton Park, Matteson, and Park Forest, original pipe that has roughened inside holds that organic film more easily, so regular cleaning matters even more. For a kitchen or bathroom drain that is also slow, how to unclog a drain walks through clearing it.
If drain flies keep coming back from a drain you can't reach, call and get connected with a local plumber - see all service areas or browse the blog.
Answers
Drain flies breed in the film of organic gunk - hair, grease, soap, and food residue - that coats the inside of a slow or dirty drain. Any drain that is used rarely, draining slowly, or overdue for cleaning gives them a damp, food-rich place to lay eggs. The flies are a sign that a drain somewhere has buildup inside it.
Find the drain they breed in with an overnight tape test, then scrub the pipe wall with a drain brush and treat it with an enzyme or baking-soda cleaner followed by hot water to remove the film holding their eggs. Repeat daily for about a week to catch newly hatched flies and break the cycle.
Bleach is not a dependable fix. Poured down a drain it mostly runs straight through without scrubbing the film off the pipe wall, so it rarely reaches the eggs and larvae clinging to the sides. Physically cleaning the pipe with a brush and an enzyme cleaner removes the breeding layer, which is what actually ends the problem.
Because the life cycle runs roughly one to three weeks, plan to clean the breeding drain daily for about a week. That catches flies as they hatch and removes the film they lay eggs in. If they keep appearing after thorough cleaning, the breeding buildup is deeper in the line than you can reach.
Not usually - most drain flies breed in ordinary buildup inside a household drain or trap. But if they keep coming from a lower-level drain despite cleaning, along with slow drains or a sewer smell, it can point to sludge or a crack in the sewer line where waste sits. A camera inspection can confirm whether the line is the source.
Keep drains clean and flowing, since they can't breed without the organic film to lay eggs in. Clean kitchen and bath drains regularly, keep grease out of the sink, run water through little-used drains to seal the traps, and use a drain strainer. Consistent drain cleaning is the whole prevention strategy.
Drain flies don't bite and are not known to carry disease into the home, so they are more of a nuisance than a health hazard. What they signal matters more: a cluster of them means a drain has a layer of organic buildup inside - the same buildup behind slow drains and odor - which is worth cleaning out.
Call now to get connected with a local plumber who can clear the buildup they breed in across Richton Park and the South Suburbs.
