A reader has been finding black worms in his toilet over the last couple of months. The worms in the toilet (we should actually say worm in the toilet, as only one is ever found at a time) appear seemingly out of nowhere, and they do not appear to be linked to anybody using the toilet. (In other words, the worms aren’t coming from somebody, which is good.) What are these black worms in the toilet? Is our reader finding a type of worm at all, or might he be finding some kind of larva (or larvae, since he’s found five)?
Before submitting his question, the reader did a decent amount of research, which we appreciate. The reader looked into moth fly larvae (also called “drain fly larvae”), but concluded that he likely didn’t find this type of larvae because they are smaller than whatever he’s finding in his toilet. The creatures in our reader’s toilet are about 3/4 of an inch to an inch long, and moth fly larvae are less than half this size, tending to be around a quarter of an inch long. On a number of occasions, we’ve written about moth fly larvae. In fact, we wrote about moth fly larvae recently, and in the context of finding them in the toilet interestingly enough. Although moth fly larvae are found in toilet bowls with some regularity, we agree that our reader probably didn’t find this type of larvae, not only for reasons related to their size, but also because the creature our reader found doesn’t look like moth fly larvae. (If you click on the link above, you will find a fairly clear picture of a moth fly larva that a reader submitted.)
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Speaking of the appearance of our reader’s find, he sent us two nice pictures:
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Based on the creature’s appearance, the reader speculated that he might have found black soldier fly larvae, and we think this is as good a guess as any (because when we saw the pictures this is immediately what came to mind). Black soldier fly larvae – which commonly go by their acronym, BSFL, and not so commonly by their scientific name, Hermetia illucens – are creatures that, like moth fly larvae, we have written about several times before. They most frequently come up in connection with certain kinds of composting operations, for which they are often used. So, when people find BSFL, they almost always find them in a compost heap (or a naturally occurring counterpart, like a pile of decomposing organic matter in the forest). For this reason, it is fairly bizarre that our reader is finding BSFL in his toilet (if indeed he is), but it’s not unthinkable, as they can sometimes be found in toilets that haven’t been cleaned in awhile, where waste has accumulated. Obviously, we have no idea what shape our reader’s toilet is in, but he did mention it was downstairs, so perhaps it escapes regular cleanings. If the toilet is in need of cleaning, then it ought to be cleaned to get rid of the BSFL, which our reader expressed interest in doing.
Unfortunately, we can’t be sure the black worms in the toilet our reader found are black soldier fly larvae. They normally aren’t in toilets, unlike moth fly larvae and other similar creatures, such as black scavenger fly larvae, which is another type of creature we considered in the course of writing this article, but they don’t really look like our reader’s find. On the other hand, the pictures we were sent really look like black soldier fly larvae, so that is our best guess, and we would suggest that our reader looks into them (he can start on this site) if he cares to know more about them.