Playing dead: foxes and winter trees.
For an illustrated version, see pages 16-18 in The Environmentor Dec 2017-Jan 2018, vol. 6, no. 3.
Possum is not the only critter who can pretend to be dead, at least in folktales...
There was once a man returning home from a very good day of fishing. He had caught so many fist that they covered the bed of his wagon! He was looking forward to a big fish dinner, and then smoking fish to last the winter.
But a hungry fox, looking down from a hilltop, spotted his delicious load and quickly made a plan. She dashed ahead and lay down flat in the road, careful to hold absolutely still.
When the man drove up with his wagon, he saw the fox. "Oho, poor dead foxie. But what beautiful fur -- not a mark on her! There are no flies buzzing around: she must have dropped dead just a few minutes ago." The man stopped his wagon. "That fur could make me a hat and mittens." So he picked up the apparently dead fox, threw her into the bed of his wagon, and drove on.
But Fox was not dead. Silently she got up and began throwing fishes out of the wagon! With the last one in her mouth, she leaped down and escaped into the tall grass. After a good snack, she went back along the road and picked up more fishes.
Meanwhile, the man arrived home and called out to his wife, "See what good luck I had today! A wagon-load of fish and a fox fur too!"
But when they looked, the wagon was empty.
In winter, trees certainly appear to be dead. Like Fox, they hold still and don't do anything. A leafless forest looks like a wasteland. How depressing!
But it is just pretending to be dead. The trees are really dormant ("sleeping"), hunkering down until reliable mild weather returns.
They don't just doze off. To go dormant, they have to work through a process called "hardening."
The lethal thing about freezing temperatures is the ice crystals that can form inside cells. Daggers of ice can pierce membranes, breaching subcellular compartments and leaking precious cell fluids to the outside. Not only are the cells' innards scrambled, but also any tissues whose structural support depended on sacs filled with water ("vacuoles") will sag and flop over -- permanently. How to prevent this?
In the trunks and branches, the living cells under the bark get rid of as much water as they can. They pump it out into the spaces between cells. The remaining cell fluids become so syrupy and concentrated that they act like antifreeze! Meanwhile, the water in the intra-cellular spaces is so ultra-pure that it can super-cool down below -40F before it will freeze. Hardened trees can survive the up&down temperatures of an Oklahoma winter. And fortunately they depend on shortening day-length, not our unreliable autumn temperatures, to tell them when to get ready.
Deciduous (leaf-dropping) trees prepare for the cold by jettisoning their most vulnerable tissues: the leaves that they had worked so hard to produce in the spring. By autumn, the leaves have finished their work of capturing the Sun's energy and feeding the tree. Unlike the leaves/needles of evergreen trees, they aren't protected by thick waxy waterproof coatings, and they don't "harden" like the living cells under the tree's bark. The tree must get rid of them.
How does a tree shed those leaves? (No, the next year's leaves don't push the old ones off!) Every leaf is born with a built-in circuit breaker, a layer of special cells ("abscision zone") across its base where it attaches to the stem. When shortening daylength tells the tree that the time has come to for leaf-drop, the cells in this layer die; the layer becomes weak and brittle. In a few days all it takes is gravity, rain drops, or a blustery wind to snap off the leaf. No great loss: in a forest, the leaves will decay to compost and return their minerals to the tree's roots. And in the spot where each leaf was attached, a waterproof corky layer ("leaf scar") seals off the stem.
So the evergreens and the naked deciduous trees, hardened against the worst winter can bring, "play dead" while they sleep. No fish dinner awaits them, but they will feast on sunlight when spring comes again.
Folktale motif K371.1
In Europe and Japan there are many stories about Fox pretending to be dead, tricking people who want more than they have. Native American Nations also tell about a predator (Bobcat, Raccoon, etc) who pretends to be dead so that prey (Turkeys, Crayfish, etc) will come close enough to grab. There are advantages to being able to play dead!
My retelling is based on Judit Bodnår, A Wagonload of Fish (Hungary) Lothrop Lee & Shepard 1996; Myra Ginsburg, One Trick Too Many: Fox Stories from Russia, Dial 1972. Variants are known from Ireland and Finland to Russia.
I am inspired by Hope Jahren's essays in Lab Girl (Alfred A Knopf 2016), especially pp 95-96 and 191-193.
For a fine microscopic view of an abscission zone see