A very friendly reader by the name of Warron wrote to us recently to ask about a worm he found. Helpfully, he included a nice, large photo of the worm, which you’ll find below. The worm is black, or possibly a really dark brown, and it appears to be rather long, although it is hard to be certain of this because there isn’t an object by which to approximate the length of the worm. What is this (possibly) long, black worm?

As always, it is very hard to be sure what type of worm are reader is dealing with, even with the photo he included. As we mentioned, it’s not clear exactly how large this worm is, and we also don’t know what part of the world this worm is from. Moreover, was the worm found in the soil, or was it found in an aqueous environment? We simple don’t know, and that makes identifying this worm difficult.

At first, we thought we were looking at a run-of-the-mill earthworm (and in fact there is a good chance we are). Earthworms tend to be light brown, or they tend to be a light brown relative to the color of the worm featured in the picture, but this isn’t universally true. A quick search for images of earthworms reveals that these creatures can in fact be a dark brown or almost black color (there are several different species of earthworms, after all), just as our reader’s worm is. However, it doesn’t appear that the worm in the picture has a clitellum, a thickened section of the body wall of earthworms and leeches. Clitella (the plural form of “clitellum;” say what you want about Latin being a “dead language” – it comes in handy) look a bit like bands wrapped around earthworms, and they tend to be in the center of their bodies, lengthwise. In the picture above, there is thickened section in about the middle of the worm, but normally the clitellum is more easily discernible.

The worm our reader found also looks a bit like one type of worm people commonly find in their aquariums, namely, ribbon worms. One type of ribbon worm – Notospermus tricuspidatus – is long and black, although this particular kind of ribbon worm has a white “W” on its heads. Given that this worm is photographed out of water, we doubt our reader found it in an aquarium, but if he did, he might have come across some species of ribbon worm.

If our reader didn’t find a ribbon worm, it seems likely that the worm he found, whatever it may be, belongs to the subclass of animals known as Oligochaeta, which is part of the annelid phylum. There are many different worms, both terrestrial and aquatic, that belong to the Oligochaeta subclass, including earthworms. Again, we can’t be sure of this, but it’s a good guess given that our reader’s worm looks a lot like an earthworm.