Reptiles, amphibians, land snails, numerous insects, and some of the mammals pass the long northern winter months in a strange torpid condition known as hibernation. Frogs and most turtles bury themselves in the mud and vegetation at the bottom of a pond or stream, emerging when the ice breaks up in early spring. Toads bury themselves in the ground, digging their way backward with their horny heels. Some mosquitoes hibernate. Most insects, however, go through winter in the egg, larva, or pupa stage.
Few mammals migrate seasonally.
Some species of bats do but others hibernate in caves. Rabbits, squirrels, foxes, muskrats, mink, weasels, field mice and deer mice are present and active all winter. The bears, skunks, raccoons, possums and chipmunks store up thick layers of fat and go to sleep in their dens when the severe cold comes. But they are light sleepers and on mild winter days are likely to awaken, come out, and move about. Other mammals, however, truly hibernate.