A few days ago we received a question from a reader who sent us a picture of what appears to be a red caterpillar with eyes. (Just a few days ago, we answered a question about a yellow worm with eyes, and the “worm” in question was in fact a caterpillar, so evidently people are seeing lots of caterpillars with eyes recently.) Along with the picture, the reader asked one question (slightly edited for clarity): “What kind of animal is in the photo?” Presumably, he is wondering what the red caterpillar with eyes is, so we will limit ourselves to the matter of identification.

First, here is the picture our reader submitted:

The picture clearly shows a caterpillar that appears to have two large eyes. What kind of caterpillar we are looking at is of course the question, though.

First, we should note that the caterpillar’s eyes are not in fact eyes. Rather, they are eyespots, which serve as a defense mechanism for caterpillars and various other animals. More precisely, eyespots are a form of mimicry, whereby the caterpillar’s (or other animal’s) eyespots look like the regular, functional eyes of another animal. The presence of eyespots can make the caterpillar appear inedible or dangerous to predators. The caterpillar above looks a bit like a snake, for instance, and this could scare away birds. Unfortunately, though, eyespots are quite common on caterpillars, so the most notable feature of the caterpillar pictured above doesn’t get us very far with respect to identification.

In general, and as we have pointed out many times before, caterpillar identification is extremely difficult because of the vast number of different species. There are about 175,000 species in the Lepidoptera order, which is made up of moths and butterflies, and hence there are about 175,000 species of caterpillars. (Caterpillars are the larval form of moths and butterflies.) Of course, not all caterpillars are as widespread as others, and some caterpillars are found a lot more frequently than others. For this and other reasons, we think our reader might have found a type of Swallowtail caterpillar, which make up the family Papilionidae.

Swallowtail caterpillars are found all over the world, and the two types of Tiger Swallowtail caterpillars (Eastern and Western) are commonly found across the United States. (For the record, we have no idea where our reader found the caterpillar, which is another reason why it is difficult to narrow down the range of possible species he found.) There are well over 500 species of Swallowtail caterpillars, and not all of them have large eyespots, but a number of them do, including both the Eastern and Western Tiger Swallowtail caterpillars. These caterpillars are either brown or green, however, so we don’t think he found one of these two species. However, given the physical resemblance between the caterpillar pictured above and other Swallowtail caterpillars, it seems reasonable to assume our reader is dealing with a caterpillar in the same biological family.

This is only a possibility, though, and we don’t want to imply we are overly confident in this suggestion. It certainly strikes us as a live option, but we of course aren’t certain, and this is just the way caterpillar identification is. Hopefully we’ve at least guided our reader in the correct direction, allowing him to research the caterpillar more if he is so inclined.

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