The Alaskan wood frog (scientific name: Lithobates sylvaticus) is an amphibian that commonly inhabits the range from North America to the Arctic Circle. Adult wood frogs are about the size of a palm, their lifespan is from 4 to 6 years. Because they have to live in areas with cold environmental conditions, they have developed a very special cold tolerance strategy: “Stop living” to overcome the cold.

This frog also sets the record for the best cold tolerance among vertebrates when it can “petrify” for about 7 months at an average temperature of -14.6 degrees Celsius, even -18 degrees. C, according to National Geographic .

When it begins to feel the cold of winter, the wood frog will stop all vital functions, from heart beat to brain activity, and let the body freeze on its own. Ice begins to form when ice crystals touch its skin.

Molecular mechanisms allow the wood frog’s body to carry out this process efficiently. Their liver is able to break down glycogen compounds into glucose (sugar) and pump it straight into the bloodstream. This is essential because the high glucose content in the frog’s cells helps them survive the long cold winter.

The main function of glucose is to hold water inside the cell. Frostbite in humans is caused when the water in our blood turns to ice. That fluid thickens around cells and tissues, thereby drawing water out of the cells. Eventually, the cells become dehydrated and the person dies. By making cells “super sweet” with glucose (the sugar circulating in the blood), frogs keep their bodies hydrated. In particular, scientists discovered that wild frogs have Glucose concentrations in muscle tissue, heart tissue, and liver tissue were dozens of times higher than in frozen laboratory frogs.

When the wood frog is frozen, all the organs in the body stop working. It doesn’t use oxygen anymore, has no breath, has no heartbeat, but appears to be dead. According to records, wood frogs can survive in a frozen state for 7 to 8 months and come back to life but unharmed.The arrival of spring creates conditions for wood frogs to defrost.

When spring arrives, warm weather will gradually defrost the frog from the inside out. Its heart started beating again, its brain worked. However, the scientists said, despite the regeneration, the wood frog also has to go through a “repair” phase. When the ice has just melted, the frog cannot immediately move quickly, but its body needs to replace the damaged cells.

Studying the ability of this frog to “temporarily die by hypothermia”, experts also said that urea – a waste product in the frog’s urine plays a role in helping them survive the freezing stage. Perhaps, the proteins that stick to the inside and outside of the cells have kept them from shrinking to exhaustion, thereby resisting the cold.

It is known that in addition to wood frogs, there are four other types of frogs that can also withstand cold environments: Cope gray tree frog, eastern gray tree frog, spring peeper tiny tree frog and western chorus frog.