Via the All About Worms Facebook page, we recently received a question about a “kind of worm” that appears to have two eyes. Overall, the worm is yellow, but on one end of its body it has black spots that look exactly like eyes. The eyes on the yellow worm are quite large, to the point that they look somewhat cartoonish. The reader sent a superb picture of the creature and only asked what kind of worm it is. So, we are tasked with a question of identification: what kind of worms are yellow and have large eyes?
First, here is the picture our reader sent in:
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The worm almost appears to be posing for the camera, gazing directly into the camera with its big, black eyes. The only problem with this scenario is that the worm actually doesn’t have eyes, and in fact it isn’t a worm. Rather, it appears to be a caterpillar with eyespots. Eyespots are present on many types of animals and are an example of mimicry. (The eyespot appears to be the eye of another animal – that is, the eyespot “mimics” a regular eye.) On caterpillars, eyespots can divert predators like birds from attacking because the caterpillar looks like an inedible or potentially dangerous creature. So, we can tell our reader she found a caterpillar with eyespots, and not a worm, but this isn’t terribly specific.
And unfortunately it is hard to be much more specific because of the enormous diversity of caterpillars. Caterpillars are the larval form of moths and butterflies, who are the members of the Lepidoptera order, which is comprised of around 175,000 species. To be sure, not all of these caterpillars have eyespots, but this is a common defense mechanism, so eyespots aren’t exactly a sure way to positively ID any given caterpillar species. (There is actually a really well-run, professional blog about caterpillars and eyespots, and looking around this site will give you an idea of the diversity of the phenomenon.)
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One especially common caterpillar with eyespots that we have written about before is the Tiger Swallowtail caterpillar. These caterpillars are brown during most of their instars (i.e., developmental stages), but they take on a green color during their fourth instar. The creature above looks more yellow than green to us, and no matter what it isn’t a vibrant green color (the mark of many Tiger Swallowtail caterpillars), but it does have a faint greenish hue, so conceivably our reader found a Tiger Swallowtail caterpillar during its fourth instar and captured it under strange lighting. We aren’t at all confident in this answer, though, and the plausibility we would assign to it depends on other factors, like the geographical location in which the caterpillar was found. We mention it as a possibility primarily because Tiger Swallowtail caterpillars are extremely common and people have written us questions about them a few times before. It is also possible she found another type of Swallowtail caterpillar (there are hundreds of species), like the Spicebush Swallowtail caterpillar. These creatures are generally green, but they can turn a yellow color before pupating.
Unfortunately, we aren’t sure what the yellow worm with eyes is, but we are confident it isn’t in fact a worm with eyes. It is almost certainly a caterpillar with eyespots, and hopefully this will at least partially help our reader. If anyone has identification suggestions, please feel free to leave a comment below.