Avoiding the Big Freeze - Animals in the Cold - Forest Barkdoll-Weil Fine Art Photography

Avoiding the Big Freeze - Animals in the Cold

A spider, about 1 centimeter long, traveling on the snow at -2°C (28°F)

Imagine a tiny spider no more than a centimeter long. Winter is in full force, and the spider’s body temperature is below freezing as it slowly crawls across the snow. Yet, the spider continues on, unperturbed. How does it avoid an icy death?

The price of staying warm

We mammals take for granted the luxury of being warm-blooded (homeothermic),¹ and we are pretty good at maintaining a constant body temperature despite cold surroundings.² However, if our temperature drops much below 95° F (35° C) hypothermia can become life-threatening.

A non-homeothermic animal that allows its body temperature to fluctuate widely with the surrounding environmental temperature is called poikilothermic. Benefits of poikilothermy include tolerating a much wider range of temperatures and requiring less energy (food) than endotherms to fuel the internal “fires” that warm them.³ However, poikilothermy alone doesn’t protect the animal from freezing when the temperature drops too low.

To freeze or not to freeze

When water freezes it expands and can form sharp crystals. If this occurs within body tissues, particularly inside cells, the tissues and cells may become irreversibly damaged, killing the animal.⁴

Poikilothermic animals confronted with the prospect of freezing temperatures have several options to prevent fatal ice crystal formation. They can avoid the low temperatures like some frogs that hibernate in ponds protected by the water⁵ or monarch butterflies that migrate to warmer climates. Alternatively, they can evolve a way to adapt to the freezing temperature.

Crystal clear

Water can remain as a supercooled liquid down to nearly -40°C (-40°F) if there are no ice “seeds” or nucleating particles present.⁶ Many animals can also supercool by eliminating ice nucleating particles like food and bacteria from their guts. Certain aphid species have elevated this skill to an art form and can survive temperatures below -20°C (-4°F). Cold tolerant animals often combine masking or removing ice nucleating particles with other adaptation mechanisms.

Freeze avoidance - the antifreeze option

Antifreeze substances, like the ethylene glycol in your car, act by lowering the temperature at which a liquid freezes. Many arthropods including some insects, spiders, and ticks use the sugar-alcohol glycerol to supercool, some being capable of surviving at 40 degrees centigrade (and Fahrenheit⁷) below zero. These freeze-intolerant animals will die if they freeze.

Antifreeze proteins are also widespread in animals ranging from fish to arthropods and can dramatically lower the freezing point, allowing the animal to avoid freezing and remain active.

Being supercooled is not risk free (although it may be super cool!). Water in a supercooled state will rapidly freeze if an ice seed is introduced. A supercooled animal can experience similar rapid, and fatal, freezing if exposed to ice seeds and will often combine antifreeze with ice seed control like the aphids mentioned above.

Embrace your inner ice

Some animals avoid catastrophy by allowing freezing to occur but in a controlled and highly regulated manner – they are freeze tolerant. The wood frog can survive being frozen solid at -6°C (21°F) for a month, the goldenrod gall fly to -40°C (-40°F), the fire-colored beetle survives to -26°C (-15°F), and the bald-faced hornet queen to -14°C (7°F). Even the woolly bear caterpillar, despite being a poor predictor of winter severity, can survive being frozen to below -10°C (14°F).

Interestingly, a parasitoid wasp that preys upon the gall fly larva is freeze-intolerant – two different insects in the same tiny chamber using different cold adaptation strategies.

Nothing in life is free

Staying alive in the cold has costs, and most poikilothermic animals don’t maintain their cold-adapting machinery year round. Within 12-24 hours of the onset of freezing, wood frogs begin producing large amounts of the sugar glucose, up to 100 times the normal amount, which draws water out of the frogs’ cells and organs into non-critical spaces such as under the skin where it can safely freeze. Upon warming, the frogs rapidly metabolize the glucose.

The trigger for wood frogs to engage their freezing machinery is the freezing of their extremities – fingers and toes. Finally, after pumping glucose-containing blood to other organs and tissues, the frogs’ hearts stop beating, leading to the wood frog motto, “Cold hands, cold heart,” contrary to the similar human saying.

Freeze tolerant and freeze intolerant arthropods need time to prepare their cold adaptation machinery – sugar alcohols and antifreeze proteins – as cold weather approaches; they lack the protection of these molecules during warm months. Deprived of this time – for example, during a sudden, harsh cold snap – many will freeze and die if they can’t shelter in a warmer location.

Why bother with cold tolerance?

Adaptations to freezing are widespread among animals – for example arthropods, fish, reptiles, and amphibians – so living in freezing climates must have benefits. The most basic is survival – if you live where it freezes you must adapt. Additionally, certain predators may be less active or may have migrated to warmer climates; cold tolerant species may be able to extend their range into colder climates than cold intolerant animals; and it may be an advantageous breeding strategy.

Consider the wood frog that is one of the earliest frogs to breed. Unlike underwater-hibernating frogs who experience slower and less dramatic temperature changes, the wood frog thaws quickly in response to warming weather and is able to get a head start in breeding and producing tadpoles. This allows wood frogs to take advantage of transient bodies of water like vernal pools that later breeders are unable to exploit.

“It did not lead him to meditate upon … man’s frailty … able only to live within certain narrow limits of heat and cold. ” – Jack London, To Build a Fire

Despite attempts to engineer cryogenics enabling humans to be successfully frozen and thawed at a later date – perhaps after a disease has been cured or as a step toward increasing our life spans – cold tolerance approaching that of these animals is still out of our reach.

In the meantime, the next time you are out in subzero weather give a nod to all the cold surviving animals around you.

Notes

1 Many animals are homeothermic – they keep their body temperature within a narrow range. Mammals and birds are also endothermic and maintain their body temperature primarily with the heat produced by “burning” energy from food. Some reptiles can also maintain their body temperature by behavioral thermoregulation, for example, by moving between warm and cool spots to keep an optimal temperature.

2 Marine mammals, such as seals, show only minor decreases in core temperature even after long, deep, Arctic Ocean dives. The “Ice Man” Wim Hof, although not a marine mammal, can also maintain his internal temperature while immersed in ice water for extended periods.

3 Early Antarctic explorers required 7,000 to 10,000 daily calories compared to 2,000-3,000 normally. This increase was largely due to the energy requirements for staying warm in such a cold environment.

4 The power of freezing water is familiar with anyone who has had a pipe burst in winter or has left a bottle of beer in the freezer by mistake.

5 Pond water won’t get much below 0°C (32°F) and will protect the frog as long as the pond doesn’t freeze solid.

6 At moderate sub-freezing temperatures ice formation occurs in the presence of nucleating particles – dust, bacteria, etc. See my article Crystalline Entities – Snow, Hoarfrost, and Rime Ice at https://forestbarkdollweil.com/snow-crystals-hoarfrost-rime-ice/

7 -40°C = -40°F

8 Humans being warm-blooded take the opposite approach, “Cold hands, warm heart.”