A reader recently sent us an excellent photograph of what appears to be a Tiger Swallowtail caterpillar. The reader was only wondering what kind of “worm” she found, so we’ve already answered her: she didn’t find a worm, but rather a caterpillar, and we are pretty sure this caterpillar is a Tiger Swallowtail caterpillar. However, we can’t just assert this without giving any explanation, so we’ll quickly supply one and then come to a speedy conclusion.

First, here is the picture our reader sent:

Our first reason for thinking this is a Tiger Swallowtail caterpillar is that it looks exactly like one. (Come to think of it, this is also our only reason for thinking this, but it’s a good reason.) We’ve answered questions about these caterpillars several times, and for whatever reason people always seem to submit good photographs along with their questions. A couple found a Tiger Swallowtail caterpillar that they wanted to show to their grandchildren, but weren’t sure what it was and sent a nice photo of one in a bag. Another reader sent a close-up shot of “a green caterpillar with eyes,” which she was quite terrified of, so she also wanted to know what she found. (The two spots that look so much like eyes are in fact not eyes, but rather eyespots, which help the caterpillar looks like something other than a caterpillar as a defense mechanism.) So, at this point we are confident that we know a Tiger Swallowtail caterpillar when we see one. We weren’t always so well-acquainted with these caterpillars, however, as it was actually a comment from a reader that first called our attention to these types of caterpillars, to the Eastern Tiger Swallowtail caterpillar, more precisely. (This article has two great pictures of the creatures.)

We aren’t sure of the exact species of caterpillar our reader found, as several members of the Papilio genus (to which the Tiger Swallowtails belong) are essentially indistinguishable, but we presume she found an Eastern or Western Tiger Swallowtail caterpillar because they are both extremely common, at least in the United States and to some extent in North America as a whole. (The Eastern species are found on the East Coast and the Western ones on the West Coast, as you’d expect.) Both species undergo a similar maturation process that involves turning green during one of its instars (developmental stages), and it appears that the creature pictured above might be transitioning into or out of this stage. They are normally brown, which appears to be the dominant color of the caterpillar our reader found.

So, we are fairly certain our reader found an Eastern or Western Tiger Swallowtail caterpillar, and that is really about all there is to say – worm identification at its most efficient. More information about Tiger Swallowtail caterpillars, however, can be found by clicking on the links above. Hopefully we’ve correctly identified our reader’s find, and if we have, she can read to her heart’s content about Tiger Swallowtail caterpillar on this site.