Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [75]
The tent caterpillars are not endearing to most people, but the black-and-rust-red banded woolly bear caterpillars come close. They are the larvae of the Isabella tiger moth (Pyrrharctia isabella) that is specialized to overwinter in the caterpillar/larval stage. The Isabella tiger moth (formerly Isis isabella) is a member of the family Arctiidae, in which most species are beautifully colored in striking patterns of bright pink, red, black, yellow, orange, pure white, and blue while in the adult, moth, stage. The Isabella moth, in contrast to most of its group, is plain colored with predominantly dirty-yellow forewings and with a pinkish-yellow hue to the hindwings. W.J. Holland in his classic Moth Book (originally published in 1903) writes: “Both the moth and the larva are common objects, with which every American schoolboy who has lived in the country is familiar; and unhappy is the boy who has not at some time or other in his life made the country his home.”
I’m happy to report from the countryside of Vermont and Maine that the “banded woolly bear” is still familiar to most people. According to local folklore, the width of the central reddish band reflects the severity of the coming winter. However, the caterpillars subtly change color over successive molts through the summer, becoming less black and more reddish as they age, i.e., as winter approaches. When touched, this caterpillar characteristically curls up into a defensive posture with stout bristles sticking out in all directions, much like the European hedgehog. In this species as in other Arctiids, only the caterpillars survive winter.
In the fall of 2001, I picked up three woolly bear caterpillars and I wondered how they, as well as three hatchling snapping turtles that I had retrieved as they were digging out of their nest in sandy soil, might bury themselves for winter. If I let these animals loose I could, of course, never hope to find them in winter. My question was simple: Will they bury themselves in moist soil, hide under the dead leaves, or stay on top of the leaves under the snow? To find out I filled a two-gallon plastic jar with soil, put leaf litter on the soil, and then buried the jar in the woods up to the level of the soil. Within a month frosts had hardened the top layers of the soil, and the jar was buried in snow.
Woolly bear caterpillar in defensive and hibernating posture. Isabella moth at rest.
Winter was not yet over by the end of February, but whatever the caterpillars (and turtles) were going to do to prepare for it, they should have done by then, so I shoveled off the snow and pulled the jar up to examine its contents. I found the three caterpillars almost immediately. They were unfrozen and curled up just under the leaf litter. The turtles were not in sight. Due to the snow insulation, the ground was, as usual, unfrozen, and I dumped the soil from the jar to sift through it. It was difficult to find the turtles. They were caked in mud with their heads and feet retracted into their shells and tails curled alongside. They looked like muddy pebbles. I distinguished them from pebbles at first only because they were compressible with my fingers.
To find out how these hibernators might act when warmed up, I brought them all, caterpillars and turtles, inside the house. After being washed with water at room temperature, the turtles “instantly” extended their limbs and heads, started rubbing their eyes and swimming in a