Swallowtail Surprise

I’ve made it up to the end of August in my photo sorting, which means I’m now going through all the pictures I took over the two days Julia and I spent surveying for leaf-mining moths at Black Rock Forest in New York (the results of which, incidentally, you can peruse here if you like). You may recall that on the first day of the survey we bumped into a bald-faced hornet devouring a yellowjacket. One of the highlights of the second day was getting to witness the defense display of a young tiger swallowtail caterpillar. It was just sitting there on a black cherry leaf, doing a very good job of mimicking a bird dropping…


…when suddenly—maybe because it was startled by my camera’s flash—it decided to stick out its fake snake tongue!


That thing is called an osmeterium, and you can read all about it on Wikipedia. All swallowtail caterpillars have one, and the effect is particularly striking with older larvae that also have big fake eyes on their backs:


…Although maybe it’s even more surprising to have a forked tongue pop out of a piece of bird poop than out of something that looks like a little cartoon snake.

From above, this caterpillar seems to be sporting a goofy grin:


That yellow-orange “birthmark” under its right “eye” is troubling; I’m not sure what might be behind that. Anyway, the caterpillar’s real head, of course, is down below:


And if you look really close, you can see that rather than having a single eye on each side of its head, it has a cluster of five ocelli. This feature is common to all butterfly and moth caterpillars (except for a few tiny leafminers), and it’s a good thing to look for when trying to decide if you’re looking at a caterpillar or a sawfly larva (which would only have one ocellus).


About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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4 Responses to Swallowtail Surprise

  1. Judy says:

    Great pics! Interesting tale. As always, who knew? Answer: You!

  2. Ken Crowee says:

    Life is better than fiction! This is truly reality.

  3. Pingback: Pick & Mix 41 – some links to entertain and inform | Don't Forget the Roundabouts

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