“What is it in the bathroom (live, ~8-10 mm)? Best regards,” is all this reader writes in his submission regarding the black, worm-like creature pictured below. Although our reader does not give a lot of context surrounding the worm’s discovery, knowing the location it was found in, and seeing what it looks like, leads us to believe that this is a drain fly larva. Commonly known also as sewage flies, sink flies, filter flies and moth flies (due to the adult insect’s stout furry body), drain fly larvae are common household pests that show up near people’s drains, hence the name.

These critters are not directly harmful to humans or animals. They do not bite or sting, they are not parasitic, and they do not even carry disease, despite spending so much time in filth. That said, when they die and decay, they can cause allergic reactions, so we definitely suggest moving the worms outside before they get a chance to do that. And, if our reader finds larvae that are already dead, we suggest avoiding physical contact when moving them. Now, the question is, why do drain fly larvae show up in the first place? Drain fly larvae are detritivores, meaning they eat dead or decomposing organic materials, and like most detritivores that can survive in aquatic habitats, drain fly larvae love stagnant water. When a toilet, shower, bath, or sink is left unused for a long period of time, and water is not run through the pipes, lots of different creatures will be attracted to the stagnant water as algae and bacteria start to grow.

For drain fly larvae in particular, it is also the stuff growing around and inside the drain that they like to munch on. In fact, a mother drain fly will lay its eggs on the organic film that eventually forms on the lip of a drain. The best way to control, eliminate, and prevent drain fly larvae is by keeping one’s drains and bathrooms clean. Scrubbing out that film often prevents the flies from laying their eggs, and by using boiling water and cleaning agents to clean one’s drain often, tons of different species of pests are discouraged from taking up residence in one’s drains.

In conclusion, we believe our reader found a drain fly larva in his bathroom. He does not specify how many he found, so it could be a one off thing. We recommend moving any worms outside, and cleaning his bathroom thoroughly. We hope this helps, and we wish him the very best!

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