### Wood Frog
Rana sylvatica
This amphibian survives brutal sub-zero winters by turning up to 65% of its body into solid, razor-sharp ice.
The Story
Winter in the Alaskan subarctic is a death sentence for most cold-blooded creatures. But when temperatures plummet to -16°C, the wood frog (Rana sylvatica) doesn't dig deep underground to escape. Instead, it lets the cold take over, completely stopping its heart and turning up to 65% of the water inside its body into solid ice.
To a human, touching a frozen wood frog feels like picking up a frog-shaped ice cube. It has no heartbeat, no brain activity, and no breathing. It can stay in this bizarre suspended animation for two whole months, essentially pausing its life to wait out the worst of the freezing temperatures.
Then, as the spring sun warms the forest floor, the ultimate magic trick happens. The ice melts, the frog's heart suddenly kicks back into gear, and it simply hops away as if nothing ever happened.
How It Works
How does it avoid being shredded from the inside out by expanding ice crystals? The frog survives using an extreme biological antifreeze system:
- The Sugar Rush: As winter approaches, the frog stops eating and stockpiles glycogen. The second ice touches its skin, the frog's liver goes into overdrive, pumping massive amounts of glucose (sugar) and urea straight into its bloodstream. - Biological Antifreeze: This thick, sugary syrup acts as a "cryoprotectant." It actively lowers the freezing point inside the frog's delicate cells. - Safe Freezing: Because the cells are packed with this syrup, ice only forms in the extracellular spaces—the empty areas between the cells. This prevents jagged ice from puncturing cell membranes and destroying internal organs.
