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CATERPILLAR OF THE WEEK: From their early-instar gregarious cuddling habits to their late-instar rear ends stamped with smiley faces, promethea caterpillars (Callosamia promethea) indisputably rank among the most charming lepidoptera species. _____________________________________________________

Like many caterpillars, promethea generally shed their skin 4 times during their larval stage. For promethea, this involves dramatic changes in the pattern and coloration of their skin. When they hatch, they have yellow- and black-striped bodies. With their first molt, they add white stripes into the mix. Their second shed is my favorite, switching away from stripes to a whitish-green body with black polka dots and yellow baubles. After sheds three and four, their body ultimately remains whitish-green, with the addition of blue polka dots, bright red horns, and a yellow butt that sports a jaunty smiley-face emoticon.

During their early instars, promethea caterpillars are gregarious. They squeeze their striped bodies next to each other, side by side by side, from one edge of a leaf to the other, slowly crawling backwards together as they munch the leaf in unison. As they grow older, they become more solitary and their eating habits are less adorable. I become able to focus on actually getting work done, rather than watching them every moment of the day.

We haven’t had promethea caterpillars in the lab in nearly three months. So why bring them up now? With deciduous trees standing bare, late fall is a perfect time to search for promethea cocoons in the wild.

When it’s time for a promethea to pupate, she’ll build her cocoon inside a leaf. Before hunkering down for good, she wraps silk around the leaf’s petiole (the stem that connects a leaf to its twig), securing the petiole to the tree. When all the other leaves fall off the tree, hers stays stubbornly in place. So stubbornly, in fact, that naturalist Bernd Heinrich has observed cocoons in place years after they produced a moth. The silk is so strong that it can occasionally strangle and kill the twigs it’s wrapped around, as they grow thicker.

Next time you’re out for a walk, see if you can find any promethea cocoons. In New England, they’re especially common on wild black cherry trees. On a walk in the woods one frigid March morning, I discovered a tree bearing at least a dozen promethea cocoons in Western Massachusetts. They were all encased in ice from the previous night’s freezing rain and glistening in the sunlight. You can experience such a sight for yourself if you keep a keen eye out for the cocoons! Be sure to let us know what you find.

Stay tuned for the emergence of many promethea moths at The Caterpillar Lab next spring!

--Liz Kautz, TCL Education Director

"Caterpillar of the Week" will highlight a different species we grow in The Caterpillar Lab each week… or, you know, at least SOME weeks. We hope you enjoy meeting the caterpillars of New England!

More information on Callosamia promethea on BugGuide here:

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