Beating the Cold, Naturally

There are probably few more relaxing and pleasurable moments than coming in out of winter’s cold and cuddling up to the fireplace. We have built houses and furnaces and insulated clothing to beat the cold. But what about the less fortunate creatures who live outside; are they really less fortunate?

It appears that nature and evolution are not stupid. Top priority is survival, and that always means adaptation. To survive freezing temperatures, life had to flee or adapt. Many species of birds chose to flee, and like wealthy and pampered humans, spend their winters in the tropics. These creatures are certainly not less fortunate. Adaptation was more difficult, but the results are nothing short of amazing.

Hibernation is a form of adaptation where the animal’s metabolism slows down to very low levels. The body temperature drops, respiration and heart rate are lowered, decreasing the need for food and water. The animal becomes unconscious and survives on the fat stored in its body.

Animals prepare for hibernation by eating large quantities of food and seeking out a cave or protected spot to sleep in. Not all hibernating animals stay completely inactive all winter. Some animals' body contains a blood substance called HIT, hibernation induction trigger, which controls periods of waking up and eating stored foods in the den.

Bears, woodchucks, shrews and hedgehogs are commonly known hibernators, although bears wake up so often it is debatable if it really is hibernating. Frogs, and some reptiles and fish burrow to the bottom of ponds and lakes to hibernate. Less commonly known are bats. There are a few species of bats that migrate to warmer climates, but many bats hibernate. Their heart rate slows from a normal 180 beats per second, to an astonishing 3 per minute. The bat’s respiration slows from 8 breaths per second to 8 breaths per minute.

There is even a bird that hibernates. There is a southwestern US relative to our whipoorwills known as a poorwill. The Poorwill has been known to hibernate in rock crevices for months at a time. The bird’s body temperature drops from 104 degrees F to 64 degrees. Heartbeat and respiration drop to where it is only barely detectable. People have actually handled the sleeping birds without waking them.

The most ingenious adapters to the cold are insects. We often do not think about them during the winter. Many people assume they lay eggs to hatch in the spring and then die, in some cases this is true, but not all. Some aquatic insects join the frogs at the bottom, while many soil dwelling insects simply burrow deeper and live on stored food. Many beetles and flies take cover in fallen leaves or in caves, barns, etc., and enter into a state of suspended animation known as diapause. Honeybees gather in dense clumps in the hives and use wing muscles to generate enough heat to keep the hive temperature above freezing.

A more drastic measure in the insect world is called "cold hardening" where the insect enters a resting stage and empties its body of fluids to prevent freezing. There are even a few high tech insects such as beetles and moths that live in subarctic regions. These critters have adapted to the cold by synthesizing glycerol, the main ingredient in automobile antifreeze. They produce a 40 percent solution and can withstand temperatures as low as -125 degrees F.

Then there are the seemingly indestructible types that actually allow themselves to freeze. The Arctic Woolly Bear Caterpillar spends nine to ten months each year frozen to as low as -60 degrees F. During the brief warm season, the caterpillar becomes active and matures a little each season, but it might take as long as 14 years to mature to the moth stage!

We humans seem terribly fragile compared to these tough creatures that brave the cold. Still, we may have something in common. How often have we heard someone say they’d like to sleep till spring!