Freezing solid is usually the end for living creatures. Ice inside a body typically stops all life processes. But the wood frog, Rana sylvatica, defies this rule. Each winter, it allows much of its bodily water to freeze. It appears lifeless, yet months later, it springs back to life. Think of the freeze as the notable part, but the thaw is the real mystery.
When we think of freezing, we assume it slows everything down. The wood frog, however, stops completely. While frozen, it has no heartbeat, breathing, or brain activity. Remarkably, up to 65% of its bodily water can turn to ice without any vital signs. This ice forms outside its cells, in the spaces in between, allowing the frog to survive unscathed.
Janet Storey, a researcher at Carleton University, explains it best: “They look like they’re totally dead, and then they’re not.” This state is sometimes likened to “clinical death,” which involves irreversible loss of all body functions. However, the wood frog’s ability to revive after freezing illustrates the difference. It’s still a mystery what happens in the brain during this freeze.
The wood frog has a unique survival trick: sugar. Glucose prevents its blood from freezing, allowing it to tolerate blood sugar levels much higher than what humans can endure. In Alaska, these frogs undergo freeze-thaw cycles in early fall to prepare their bodies for winter. This practice seems to stimulate their glucose production.
The process of coming back to life is just as fascinating. Once thawed, the frog’s heart and brain restart on their own as the soil warms in spring. Research shows that wild Alaskan frogs can stay frozen for over 200 days at temperatures below -18 degrees Celsius, all while maintaining a 100% survival rate. The swift recovery raises questions about how vital organs resume functioning after such a long absence of activity.
The wood frog’s ability might inspire advances in organ preservation. Experts like Al-Attar and Storey see potential in the frog’s natural defenses against freezing. In the U.S., thousands await organ transplants, highlighting the need for improved preservation techniques. Although no one has successfully frozen an entire organ for revival, the wood frog gives us hope for future breakthroughs in medicine.
As researchers dig deeper into this scientific wonder, the wood frog may offer valuable insights into survival and preservation in extreme conditions—a topic garnering attention on social media and among scientists. The mystery of how it revives after freezing is an ongoing puzzle, igniting curiosity in fields ranging from cryobiology to organ transplantation.
