WINTER WONDERS

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Woolly Brrrrr

Sift beneath leaves or peek under a snow-dusted log, and you may discover a curled-up, apparently lifeless black-and-brown-banded caterpillar??the famed woolly bear said to predict the severity of winters by the lushness of its fuzzy coat. Dont give it up for dead just yet, though.

Like a variety of other overwintering creatures, woolly bears produce an internal antifreeze called glycerol that protects their vital organs from subfreezing temperatures. But more than simply preventing freezing, the woolly bear is able to endure the formation of ice crystals in its body by limiting the growth of ice to the spaces between tissue cells. Meanwhile, it produces sugars that keep its blood and cellular water in liquid form. Come the thaw in early spring, the frozen bear will rouse itself, find a sheltered place on which to spin a cocoon and pupate. In early summer, a handsome Isabella tiger moth (Pyrrharctia isabella) emerges.

Woolly bears are only one of dozens of freeze-tolerant species, including some turtles as well as many insects in either the adult, larval or pupal stage. Perhaps most astounding is the wood frogs ability to withstand being frozen without (ahem) croaking. In winter, its entire abdominal cavity fills with ice, completely encasing all its internal organs. Its blood stops flowing; breathing and heartbeats cease; its eyes turn white because the lenses freeze. And so the frog-cicle remains until the thaw, when spring quite literally returns to its step.

A Hole in the Snow

Look for a small hole in the snow at the edge of a meadow. Chances are its the exit or ventilation hole of a field mouses tunnel. On unseasonably mild days, field mice might emerge to forage for seeds or bark. But for most of the winter, they live beneath the surface in the snug snow-covered environment of thick grass, leaf litter and crisscrossing tunnels that scientists term the subnivean zone. Here, regardless of chilly winds and subfreezing air in the harsh world above, temperatures seldom dip below 32 degrees.

Safe from owls and other predators, nourished by roots and grass, and kept warm by the earth itself and an insulating snowflake blanket, these rodents prosper in winter just as well as they do in any season, with females sometimes producing as many as five young per month. The females among those babies, in turn, start producing litters of their own one month later. This ongoing population explosion produces a spring smorgasbord of bite-size protein for foxes, coyotes, hawks, snakes and other creatures, and fuels the reproductive cycles of those creatures, ensuring the perpetuation of a healthy ecosystem.

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