what is it?

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"A curious thing, Dr. Watson," a chagrinned Sherlock Holmes might say. "Most curious."

Hugh Morgan sent me the above photo. He and his grandson found the critter—measuring about 1.5 inches long—on Roaring Fork Motor Trail in The Great Smoky Mountains National Park near Gatlinburg.

He wondered, “Do you have any idea what it might be?”

My best guess is that it’s the caterpillar of a tiger swallowtail, although all the ones I have seen have been green, but here is a description I found on the Internet:

“The caterpillar of this species changes dramatically as it goes through its various molts. In the first two instars (those periods between molts) it looks just like a bird dropping. It then changes to be predominantly green with two large eyespots near the front end. Just before pupating, the larva turns dark reddish brown.”

Does anyone else have a better idea?

- Photo by Hugh Morgan