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It’s 19 degrees and snowing in my New Hampshire backyard right now. It’s tough to imagine that we’ll begin holding open hours at the lab in less than two months! At moments like this, live caterpillars feel distant. Their winter existence and survival seem so unlikely. And yet…

A variety of caterpillar species overwinter as caterpillars, even here in frosty New England. We discussed woolly bears a few weeks ago, but this week we’ll feature species that overwinter in a manner that may seem even less likely. These species spend winter right out in the open, attached to tree branches, mimicking twigs, fully exposed to the elements all winter long.

Today we have images of two such twig mimics, the Esther Moth Caterpillar (Hypagyrtis esther) and the Porcelain Gray (Protoboarmia porcelaria). These caterpillars have great adversity to contend with--not only due to the harsh winter weather, but also in the form of hungry winter predators with few dietary options.

Golden-crowned kinglets, a native New England bird species, have winter challenges of their own. They’re all-weather carnivores. You’ll never find one at your bird feeder! Weighing only about as heavy as a nickel, they’re tiny, which can accelerate heat loss. Heat loss is a problem when temperatures are well below freezing and maintaining a body temperature above 100*F is important. So where do golden-crowned kinglets get the energy to fuel their warmth? In Maine, naturalist Bernd Heinrich studied these birds’ stomachs to find an answer. Can you guess what he found?

That’s right… caterpillars! And not just any caterpillars. The kinglets’ guts were mostly full of One-Spotted Variant (Hypagyrtis unipunctata) caterpillars. A single species provided most of their winter diet! Here in Keene, New Hampshire we think golden-crowned kinglets are mostly dining on the species pictured here, although One-Spotted Variants are a less-abundant option.

There are a lot of odds stacked against this week’s Caterpillars of the Week. And yet they survive! Stay tuned as we share stories of other winter twig-mimic species throughout the week.

- Liz Kautz TCL Education Director

Each week (or at least SOME weeks!) The Caterpillar Lab features a "Caterpillar of the Week." Each featured caterpillar is a species we've raised at our lab in Keene, NH. We hope you enjoy meeting the caterpillars of New England!

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