As winter draws in and the temperature starts to fall, small mammals begin to prepare in their own familiar way for the long freeze. They eat lots of food to build up a good reserve of fat, and then slowly burn it away through the long winter months, slowing down their bodily processes to use as little energy as possible.

This is fine for creatures such as mammals that can regulate their internal temperature, but what of all the myriad creatures whose body temperature fluctuates with the environment? What about the invertebrates, reptiles and amphibians that are collectively - though erroneously - known as 'cold blooded'? How do they prevent their blood from freezing when the surrounding temperature drops below zero?

The Big Sleep

The answer for some is to find somewhere warm to sleep, deep underground, in caves and burrows. Here the temperature never gets much below 4°C due to the insulating properties of the surrounding earth and rock. Some animals hibernate under water. In fact, many insects convert to an aquatic form so that they can spend the winter completely underwater. Because ice floats, once a pond has frozen over, the ice acts as an insulating layer that prevents the underlying water from the worst ravages of the weather. This means that a pond rarely freezes all the way to the bottom, and so its water temperature is always above zero, providing a haven for hibernating animals.

The Antifreeze

Other animals, of course, cannot live underwater or dig deep underground. Many spiders, ticks, mites and insects have developed antifreeze in their body fluids, in some cases allowing the animal to not only hibernate, but to continue an active life down to -15°C. Some Canadian caterpillars have so much antifreeze in them that they can survive down to -38 °C without actually freezing.