“I found this on our water while I was filling the tub”, states this reader in her query concerning the black worm pictured below. She is not sure if they are leeches or something else, and wants to know if it is harmful.

First of all, we do not think this is a leech. It is difficult to tell exactly what this worm looks like, given that the picture is taken so far away and the resolution is not the best, but its small size and skinny body tells us that this is probably not a leech. It could technically be an immature leech, but we still find it more likely that it is something else, specifically a drain fly larva.

Drain fly larvae are pests that feed on decomposing organic materials. In their quest for food, it is not uncommon for them to crawl up people’s drains and build nests on the film that forms on the lip of a drain that has not been cleaned for a while. They are the larval form of the drain fly, otherwise known as the moth fly or drain moth (despite not being moths), and while they are not directly harmful to humans or pets, they can spread harmful bacteria. Of course, in the case that this is not a drain fly larva, and indeed a leech or something else, and our reader starts experiencing health issues, then she should immediately consult a medical professional.

That said, we do still believe it is more likely that this is a drain fly larva. Hopefully, our reader will only find the one, which she can just move outside and then be done with it. We say this because infestations of drain fly larvae can occur. If our reader were to discover that her home is infested with them (which will be obvious by a spike in larvae numbers), there are things she can do to control and eliminate the infestation. First, in order to get rid of the nests, our reader should scrub away any film that has built up in any of her drains. She should then properly clean her drains with cleaning products (bleach, for example) multiple times a week for at least two weeks, so as to get rid of the build-up of organic matter that might have been attracting the larvae in the first place. Additionally, she needs to make sure that even after this two week period, her bathroom is consistently cleaned, as this prevents the attraction of a number of organisms that could potentially crawl up her drains.

In conclusion, we think that the black worm-like creature our reader found in her tub is a drain fly larva, which poses no real health threat to her. We hope that our reader discovers no more larvae, and that this was a once-off thing, but we nonetheless encourage our reader to employ the cleaning regime above just so that she can proactively stop an infestation from starting, and so that no more of these larvae are attracted to her tub. We wish her the best of luck with her cleaning endeavors!

• 
•