This section is from the book "A Library Of Wonders And Curiosities Found In Nature And Art, Science And Literature", by I. Platt. Also available from Amazon: A library of wonders and curiosities.
The winter sleep is a very singular property of animals and plants; and, though it occurs daily before our eyes, we are not able to explain the phenomena with which it is attended. In cold countries, many animals, on the approach of winter, retire to their subterraneous abodes, in which they bury themselves under the snow, where they remain five or six months without nourishment or motion; nay, almost without circulation of their blood, which flows only sluggishly, and in the widest vessels. Their perspiration is almost imperceptible; but still they lose something by it, as they enter their winter quarters in very good condition, and are exceedingly thin when they return from them.
Some animals enjoy their winter sleep under the earth, and others are concealed beneath the snow; some for the same purpose creep into the holes of rocks, and others under stones, or the bark of trees.
Plants have their winter sleep also; for, during the period of winter, their sap flows towards the roots, and the circuls-tion of it, which is very slow, takes place only in the widest vessels. Were the expansion of the sap in winter as considerable as in summer, it would burst all the vessels, on being frozen.
Some observers have endeavoured to prove that this singular circumstance is merely accidental, and, indeed, no difference is found in the internal organization of those animals which have winter sleep, and those which have not. It is very remarkable, that this property belongs in general to animals of prey. As these have far stronger powers of digestion, and stronger digestive juices, it would appear that abstinence from food for several months would to them be hardly possible.
The common bear, the bat, and the hedgehog, have winter sleep, but the white bear has not. As the latter is secured from the cold by his long hair, he finds nourishment in the dead whales and seals which are cast on shore by the waves.
The earthworms have winter sleep; but aquatic worms very seldom. Insects, as well as their larvae, have winter sleep. Butterflies may be often seen fluttering about in the warm days of spring, after having spent the whole winter in that condition. Amphibious animals have winter sleep, those which live merely in the ocean excepted. Few birds, on the other hand, are exposed to this state. The greater part of these, on the approach of winter, retire to a milder climate, where they can find more abundant nourishment. In Iceland, the sheep have winter sleep. In that country they are suffered to range in perfect freedom. In the winter season, therefore, they may be found buried under the snow, where it would be impossible for them to remain, were they not in that condition.