The small, wriggling worms you spotted in your drain are almost certainly drain fly larvae. They’re gray, legless, about 3/8 inch (8 to 10 millimeters) long, and slightly darker at both ends. One end has a tiny tube they use to breathe at the water’s surface. They look like tiny pale maggots and are usually found clinging to the slimy buildup inside drain pipes.
What Drain Worms Look Like
Drain fly larvae are the most common “worms” people find in sinks, showers, and floor drains. Up close, they resemble small gray or off-white grubs with no visible legs. The body tapers slightly at each end, and both tips appear darker than the midsection. That darker tip on one end is a siphon, a breathing tube the larva extends above the waterline while the rest of its body stays submerged in pipe slime.
You’ll typically see them wriggling slowly in standing water, stuck to the walls of the drain opening, or embedded in a slimy film when you pull out a drain cover. They don’t move fast, and they don’t swim. If you scoop one out, it will writhe sluggishly on a dry surface.
The adults they turn into are equally distinctive: tiny moths about 1/8 inch long, light gray, with fuzzy, oval-shaped wings covered in fine hair. They’re weak flyers with an erratic, hopping flight pattern, and they tend to rest on walls near the sink or shower. If you’re seeing both the larvae in the drain and small moth-like flies nearby, that confirms the identification.
Other Worm-Like Creatures in Drains
While drain fly larvae are the most likely culprit, a few other organisms occasionally show up. Bloodworms (the larvae of midges) are bright red and thin, roughly the same length as drain fly larvae but far more vividly colored. Their red color comes from hemoglobin, the same oxygen-carrying molecule in human blood. Tubifex worms are also red or reddish-brown, threadlike, and tend to cluster together in a writhing ball. Both of these indicate stagnant, nutrient-rich water in the pipes but are less common in household drains than drain fly larvae.
If what you’re seeing is translucent, extremely thin, and barely visible, it could be a nematode (roundworm). These are harmless free-living worms that feed on bacteria. They’re far smaller than drain fly larvae and usually only noticeable under close inspection.
Why They’re in Your Drain
Drain fly larvae feed on the organic biofilm that coats the inside of pipes. This biofilm is a layered, slimy mix of bacteria, soap residue, skin cells, grease, and other organic matter. It builds up naturally over time in any drain that carries wastewater. The thicker and more established the biofilm, the more attractive the drain is as a breeding site.
Female drain flies lay eggs directly on this film. At around 70°F, the eggs hatch in less than two days. The larval stage is the longest part of the life cycle, lasting 9 to 15 days at room temperature and as few as 8 days in warmer conditions. After that, the larvae pupate for just 24 to 48 hours before emerging as adults. The full cycle from egg to adult takes 21 to 27 days, which means a single untreated drain can produce new generations continuously.
Drains that see infrequent use are especially vulnerable. A P-trap (the U-shaped bend in the pipe) normally holds a small pool of water that blocks insects and sewer gas from coming up through the pipe. But in floor drains, guest bathrooms, or basement sinks that don’t get regular water flow, that trap dries out in two to three weeks. Once it’s empty, the drain is an open pathway for flies to enter and lay eggs.
Are Drain Worms Harmful?
Drain fly larvae don’t bite, sting, or feed on human food. They aren’t parasitic and pose no direct health threat. Their presence does, however, signal a thick layer of organic buildup inside your pipes, which is worth addressing for basic hygiene. In rare cases reported in medical literature, drain fly larvae have been associated with myiasis (larvae developing in human tissue), but this is extremely uncommon and typically involves people with open wounds exposed to heavily infested environments.
How to Get Rid of Them
The single most important thing to understand is that the larvae live inside the biofilm, not just floating in the drain water. This is why the most popular home remedies fail. Bleach kills adult flies on contact but cannot penetrate the structured biofilm where larvae are embedded. New adults emerge within days. Boiling water loses significant heat by the time it travels through the drain body and only contacts a fraction of the biofilm. Baking soda and vinegar produce a brief foaming reaction with almost no actual scrubbing effect. All three approaches kill the flies you can see, and the problem returns within about three days.
What works is mechanical removal of the biofilm itself. Use a stiff drain brush (a long, narrow bottle-brush style works well) to physically scrub the inside walls of the drain opening and as far into the pipe as you can reach. This strips away the biofilm along with the eggs and larvae living in it. Enzyme-based drain cleaners can supplement this by slowly digesting organic matter, but they require repeated applications and can’t reach biofilm deep in the pipe on their own. Think of them as a follow-up, not a first step.
After scrubbing, flush the drain thoroughly with hot water to wash loosened material down the line. Repeat the brushing every few days for two weeks to catch any larvae that survived deeper in the pipe and are still maturing. Since the full life cycle runs about three weeks, consistent cleaning over that window breaks the breeding cycle completely.
Keeping Them From Coming Back
Regular water flow is your best passive defense. Run water through every drain in your home at least once a week, including floor drains, guest bathroom sinks, and utility sinks. This keeps P-traps full and flushes away early biofilm before it gets thick enough to support larvae.
For floor drains that rarely receive water (laundry rooms, garages, basements), consider installing a waterless trap seal. These are one-way silicone valves that drop into the existing drain body. They let water flow down but create a physical barrier that prevents flies, sewer gas, and odors from coming back up. Because the seal is mechanical rather than liquid, it never evaporates, making it effective during vacations, building closures, or any period of disuse.
If you’ve found larvae in one drain, check adjacent drains in the same area. Biofilm tends to build up at similar rates in nearby pipes, and neighboring drains often harbor larvae even when no adult flies are visible yet. Brush and flush all drains in the affected zone, not just the one where you first spotted the worms.