Every living thing is adapted to enable it to cope with the environment it lives in. Organisms cope with cold, winter weather in a variety of clever ways.
Invertebrates (animals without backbones) and vertebrates (fish, amphibians and reptiles) are said to be “cold-blooded” because their body temperature changes with the ambient temperature.
Low temperatures make it difficult for these creatures to remain active in winter. So how do they survive?
Since cold-blooded animals like fish, frogs, snakes and turtles have no way to keep warm during the winter, these reptiles and amphibians can slow down all their body processes in very cold weather. This is known as “diapause.” During this period the animals use up a minimal amount of their body fat and can survive for a long period of time.
Some frogs can actually freeze solid. When cold weather approaches they just burrow under the forest floor’s leaves and debris, and when freezing weather comes, much of the water in their bodies goes out. The frogs’ veins fill with an antifreeze-like mixture of sugars and sugar alcohols, and then the somewhat-dried-out frog simply freezes. While they are frozen, ice forms around the frogs’ organs, but the frogs’ individual cells remain unfrozen and intact.
They do not breathe, their hearts do not beat and there is almost no brain activity. When spring approaches and their hide-away warms up above freezing, the frogs’ frozen bodies thaw, and they come back to life. Pretty amazing!
Many reptiles and amphibians hide in the winter under stones, logs, holes, burrows and in compost heaps, where they may be safe from predators.
Water actually makes a good shelter for many aquatic animals. When the weather gets cold, they move to the bottom of lakes and ponds. There, frogs, turtles and many fish hide under rocks, logs or fallen leaves. They may even bury themselves in the mud and become dormant.
Cold water holds more oxygen than warm water, and the frogs and turtles can breathe by absorbing it through their skin.
How do they survive in a frozen body of water? Actually only the top layer of the lake or river freezes. Underneath the frozen upper layer, the water remains in its liquid form and does not freeze. The surface water freezes at 0 °C while the lower part still remains at 4 °C.
Ice does not allow heat to pass through it easily, so the freezing of the waters below is a very slow process.
At depths below 100 feet, temperatures are cold and stable. Oxygen is trapped beneath the layer of ice. As a result, fish and other aquatic animals find it possible to live comfortably in the frozen lakes and ponds.
The body fluid of an ordinary fish can solidify if the temperature of the surrounding water drops below -5 °C. Arctic and Antarctic fish have adapted to their surroundings by a type of antifreeze protein (AFP) in their blood.
Some insects migrate to warmer climates or better conditions when winter approaches. The most famous of the migrating insects is the monarch butterfly. Monarchs in the eastern U.S. and Canada fly up to 2,000 miles to spend their winter in Mexico. Many other species of butterflies and moths also migrate seasonally.
For some, there is warmth in numbers. Honey bees cluster together as the temperatures drop, and their collective body heat keeps them warm. Ants and termites stay below the frost line, where their large numbers and stored food supplies keep them fed and comfortable until spring.
Some insects find winter shelter in holes in the ground, under the bark of trees, deep inside rotting logs or in any small crack they can find.
Praying mantis survive the winter as eggs. Woolly bear caterpillars curl up in thick layers of leaf litter for winter. Black swallowtail butterflies spend winter as chrysalids (forming a protective covering), emerging as butterflies when warm weather returns. Other butterflies hibernate as adults for the winter, tucking themselves behind loose bark or in tree cavities.
Most female spiders die after laying eggs in a fluffy, whitish cocoon which is tucked away under a log or in a corner of a building. Thousands of tiny spiders emerge from the cocoon in the spring.
Some mosquitoes lay winter-hardy eggs, which lie dormant in the soil until spring.
Many mosquito species live through the winter as adults. In fall, the mosquitoes mate and the males die. The females spend the winter hidden in protected places, such as hollow logs or animal burrows.
Many insects prepare for the cold by making their own antifreeze proteins. During the fall, insects produce AFPs, which increases in the hemolymph (insect blood). This allows body fluids to drop below freezing points without causing ice damage and also lowers the freezing point, making insects more cold-tolerant. This process protects tissues and cells from damage during icy conditions in the environment. The AFPs bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be fatal. In spring, AFP levels drop again.
Other uses for AFPs
There is increasing evidence that AFPs interact with mammalian cell membranes to protect them from cold damage.
There are many applications for AFPs: increasing freeze tolerance of crop plants, and extending the harvest season in cooler climates; improving farm fish production in cooler climates; lengthening shelf life of frozen foods; improving cryosurgery; enhancing preservation of tissues for transplant or transfusion in medicine and therapy for hypothermia.