A while back, we received some pictures of a very interesting worm (or what the reader called a “worm”) from a reader. We’ve been eager to look into the creature because its appearance is so unique: the “worm” is brown with a big head (or rather a huge head), and on this large head are two dots that look like eyes. The reader asked what kind of worm he had found, but we don’t think he found a worm. It looks more like a caterpillar, albeit a very strange looking caterpillar, one that we have never seen before. So the question is: what kind of brown caterpillar did our reader find?

First, let’s take a look at the picture our reader sent because, again, the creature under examination is very cool. (Faintly disturbing for some reason, but also cool.) Here is a side view of the caterpillar:

And here is a view from the back:

As you might be able to tell, this doesn’t look very much like a worm to us, although as we always feel obligated to say, the word “worm” isn’t scientifically precise (it refers to an obsolete taxon). Just the same, in everyday speech the word “worm” has a more or less definite meaning, and it generally refers to creatures that live underground becuase they require a moist enviroment to survive (e.g., a nightcrawler).

That said, we think this is some sort of caterpillar, although we did briefly look into slugs first. Most people think of slugs as having two “feelers” where the slug’s “eyes” can be found (in fact, these are optical tentacles with light-sensing eyespots), but of course there are many different kinds of slugs, and not all of them look like this. Indeed, some of the larger species of slugs look kind of like the creature in the picture, but we found no slugs that had a similar enough shape and body structure to the creature above. So, again, we think the reader found some sort of caterpillar.

Any time we are given a question about caterpillars we get nervous. There are tens of thousands of different kinds of caterpillars (which, by the way, are the larval form of moths and butterflies), making them exceedinly diffiuclt to correctly idenify, and we must confess we are having some difficulty finding any sort of match for the creature pictured above. At first, we thought it might be an Elephant Hawk-moth caterpillar (Deilephila elpenor) because these caterpillars have big heads, but the two creatures definitely don’t look exactly the same, in part because the Elephant Hawk-moth caterpillar has more green on its body. (However, their bodies do have some brown, and in fact the pupae of the Elephant Hawk-moth are brown.)  The other similarity between the Elephant Hawk-moth caterpillar and the creature above is that they both have patterns on their heads that resemble eyes (but aren’t actually functioning eyes). For reasons that aren’t entirely understood, this frightens away predators (like birds) that might otherwise prey on the caterpillars, making these faux eyes a defense mechanism. Again, though, the eye-like patterns on the Elephant Hawk-moth caterpillar are different from those found on the creature pictured above.

Unfortunately, we just aren’t sure what kind of creature our reader found. It looks like a caterpillar (as opposed to a worm or slug), but we can’t say much else about it. As always, we invite readers to provide suggestions as to what kind of creature our reader might have found. Just drop a comment below.