Bathroom Flies: Why Are They Crawling Out of Your Drain?
Those small, erratic flies emerging from your sink drain are not random invaders. They are connected to a complex, slimy ecosystem deep within your plumbing. Discover what these creatures feed on and why they are so drawn to the damp environment.
Drain flies, sometimes called moth flies, are observed near sinks and toilets, with one common species being *Clogmia albipunctata*, which features white markings on dark legs. These flies initially enter structures through cracks in older pipes or through pipes that have rusted or cracked due to ground shifting. The larvae of these flies establish themselves by laying eggs within the slime coating the inside of the pipes. This substance, known as a biofilm, is a living matrix composed of bacteria, fungi, and various microorganisms that accumulate from washed-down materials like hair, saliva, and food particles.
The mechanism attracting these flies is chemical. Entomologist Greg Curler noted that the flies utilize their antennae to perceive gases emanating from the accumulated biofilm over time. These detectable gases act as a powerful attractant, drawing the flies toward the source deep within the plumbing. While the larvae consume this biofilm, the adult flies themselves do not feed on household waste; they only consume small amounts of liquid and tend to remain localized, only flying great distances when seeking a new location to deposit their eggs.
A common misconception is that these flies pose a significant health risk by spreading bacteria. However, the passages clarify that drain flies are unlikely to land on people, toothbrushes, or food, and they do not actively seek to consume or lay eggs in such items, unlike houseflies or blowflies. Furthermore, while drain cleaner might offer temporary relief, Matthew Fields, who studies biofilms at Montana State University, points out that the biofilm itself is difficult to remove. This slime is created by microbes producing a sticky mixture of proteins and carbohydrates that envelops and shields them, meaning some biofilm will always persist to draw the flies back.
To effectively manage the issue, scrubbing the biofilm is recommended by Fields. Because the areas inside pipes where these flies reproduce are usually inaccessible for thorough scrubbing, some biofilm remains, maintaining the attraction for the flies.
Source: Why Does This Fly Live in Your Bathroom? | Deep Look
