The presence of small, worm-like creatures in moist areas of a home, such as sinks, showers, and tubs, can be unsettling. These organisms, commonly referred to as “drain worms,” are not true worms but are the larval stage of a small insect. They indicate a buildup of organic material within the plumbing system. Understanding this pest is the first step in effectively managing their population.
Identifying the Larvae
The organism commonly seen in household drains is the larva of the moth fly, also known as the drain fly (family Psychodidae). These larvae are small, typically growing to about one-quarter to three-eighths of an inch. They are worm-like, gray or tan, and have a segmented body structure.
The larvae are legless and lack distinct eyes, characteristic of fly larvae developing in dark, submerged environments. They use a respiratory siphon at one end to breathe while submerged in the drain’s gelatinous film. The entire life cycle, from egg to adult fly, takes eight to twenty-four days, depending on conditions. While they develop in unsanitary conditions, they are primarily a nuisance pest and are not known to pose a direct threat to human health.
Why They Thrive in Plumbing
These larvae thrive in plumbing due to the presence of biofilm, which is their sole source of food and shelter. Biofilm is the slimy, gelatinous layer adhering to the inner surfaces of drain pipes, traps, and overflow areas. This film is a rich mixture of organic matter, including hair, soap residue, fats, grease, and microorganisms.
The biofilm provides the larvae protection from water flow and most cleaning chemicals poured down the drain. Adult moth flies seek these moist, organic-rich environments to lay egg masses, depositing 30 to 200 eggs at a time. Slow-draining pipes and standing water exacerbate the problem, creating the ideal conditions for eggs to hatch and larvae to develop.
Eliminating Drain Worms
Effectively eliminating an infestation requires focusing on the complete removal of the biofilm, as chemical solutions often fail to penetrate this protective layer. The effective first step involves physical removal of the sludge from the drain opening, stopper, and overflow areas using a long, stiff brush or pipe cleaner. This manual scrubbing breaks up the gelatinous film that harbors the eggs and larvae.
Once the biofilm is disrupted, a treatment can address remaining material deeper in the pipe. Enzyme-based drain cleaners are preferred because they contain beneficial bacteria that break down organic matter, digesting the larvae’s food source without damaging plumbing. Following cleaning, pouring very hot water (not boiling) down the drain helps flush away loosened debris and remaining organisms. Boiling water is avoided to prevent potential damage to pipe materials like PVC or older porcelain.
Prevention
Long-term prevention requires regular maintenance to discourage biofilm re-establishment. Weekly flushing of drains with very hot water keeps the organic film thin and less hospitable for adult flies. Ensuring drains flow freely, without clogs or standing water, eliminates the moist, stagnant conditions flies seek for reproduction. Regular cleaning removes the food source, which breaks the moth fly’s life cycle and prevents future infestations.