Wednesday, May 22, 2013

A Winter-weary Wollybear

Spring woolybear caterpillar "Pyrrharctia isabella" (c) John Ashley
An ant inspects a woolybear caterpillar that only recently defrosted

Did you ever feel "cold to the bone" last winter? Then take a moment to admire the woolybear caterpillar. It's the larval stage of the Isabella Tiger Moth (Pyrrharctia isabella). I found this one scampering around in the yard a couple of days ago. I've seen hundreds of woolybears before, but never one this dull in color.

In these parts, woolybears have two generations each year. One set of caterpillars pupates into adult moths in summer. These short-lived moths lay eggs that hatch into a second set of caterpillars in fall. It's this second set of caterpillars that does something quite amazing.

Each fall, wollybear caterpillars curl up under rocks and logs and literally freeze solid. All winter. No heartbeat, no breathing, no sign of life remaining. In the spring they simply defrost and return to the business of eating. They'll soon pupate into the adult moths that lay the eggs for the summer generation of caterpillars.

I can tell you're not impressed. Then how about this?

Farther north, in the arctic, wollybears remain in the caterpillar phase for 14 years before they have grown enough to pupate into an adult moth. That's 14 winters worth of freezing solid. And all of this effort produces a moth that only lives for 1-2 weeks.

That's an amazing feat for any animal to pull off, but especially a two-inch long insect. Next winter when you're curled up close to a crackling campfire, raise your coffee cup to these little guys, frozen solid somewhere beyond your frostbit backside. It's bound to make you feel a little warmer inside.

Check out these three short videos of woolybear caterpillars freezing and thawing in the arctic, filmed as part of the amazing "Frozen Planet" series on Discovery.