Here’s the caterpillar!

October 5, 2014 • 1:30 pm

Did anybody spot the caterpillar? It’s out there in plain sight, I tell you!

It’s circled below. If you couldn’t see it, what do you think the chances are a bird would?

These photos and their explanation are from Mark Sturtevant, who posed the puzzle earlier:

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The hidden caterpillar is of course the mature larva of the giant swallowtail butterfly (Papilio cresphontes). The giant swallowtail is the largest butterfly in the U.S., and is a truly magnificent insect that always takes my breath away. I found larvae feeding on a type of prickly ash (Xanthoxylum americanum) which is one of its favored woodland food plants. Finding larvae of this species was one of my bucket list items, and so it was a great thrill for me. I now have several pupae, and I am looking forward to when the butterflies emerge early next summer.

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The mature larva are generally found on branches, but their markings are a bit puzzling. Although they are camouflaged to look like bark when viewed at a distance, they seem to take on a different appearance when seen up close. They have a distinctly swollen thorax with folds (eyelids?) over what looks like false eye spots. They also have iridescent rings of color on their skin. Some think that the mature larvae are mimics of a snake head, complete with glistening scales.

Other species of swallowtails (like the larva of the tiger swallowtail and the spicebush swallowtail) really do seem to be snake head mimics. Deception in the animal kingdom is a marvel of evolution by natural selection, and perhaps our giant swallowtail larva is an example of an evolving deception that has not progressed as far. Fully formed deceptions are very interesting, but cases of partially formed deceptions are valuable evidence for evolution.

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They may not be great snake-head mimics, but giant swallowtail larvae are excellent bird dropping mimics in their earlier instars. Here, they go for broke trying to look like big, wet and gooey bird droppings that landed in the middle of a leaf. They are perfectly dry to the touch.

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19 thoughts on “Here’s the caterpillar!”

  1. Damn…I would have never spotted it since I still can’t really see it after it was pointed out. I do think D. Taylor spotted it from his/her description.

    Thanks for the close-up shots of the caterpillar. Very cool.

    1. Thanks, but I didn’t spot it. Can hardly spot it now! My caterpillar looked like a caterpillar.

      “Her” description, by the way. I’m Dorothy. Hi Mark.

  7. So the story is that I was exploring some woods a few miles from my house, when I happened upon a beautiful female giant swallowtail flying rather slowly, checking out the shrubs. She entered a forest clearing, and briefly landed on a plain little bush before flying away. I immediately examined that area of the bush and found an orange giant swallowtail egg. So I had finally stumbled upon their local food plant! Within the week I had located a few dozen prickly ash bushes, and nearly as many eggs and young larvae. I spent many hours in those woods this summer, stalking and photographing my little caterpillars and other insects.

      1. “…of a wonderful insect comma…”

        (But who knows what kind of pics the caterpillar might have had?)

      1. The close up shots are not at the same angle as the first picture, but I do not think there is a rule on that.

        1. Aha! Thanks for clarifying.

          I always thought the “rule” was that the enlargement was an enlargement of the actual photo. I could see something in the circle that resembled the caterpillar (the “bird-droppings” look) but was puzzled that the photos didn’t seem to match.

  9. Caterpillar? Naw, this is a Cobbsian delusion. Must be contagious. MC has passed it on to MS.

  11. Add my vote for snake-mimicry. The pale stripe below the ‘eye’, and pale dorsal markings narrowing downwards on the sides, are reminiscent of the Copperhead (Agkistrodon contortrix). On closer inspection, there’s even a loreal (heat-sensing) ‘pit’ visible in the close-up, right where it should be. In a general sense, the distribution and habitat seem a pretty good match, and Copperheads do climb trees sometimes. Guiher & Burbrink (2008) estimate that A. contortrix is about 6.6 my old (and morphologically conservative among pitvipers, i.e. a slow-moving target); the terminal branch leading to Papilio cresphontes may be somewhat older based on calibrated trees in Zakharov et al. (2004), so there could have been time for selective tweaking of details.

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