Each September, the wood frogs of Alaska do a very strange thing: They freeze. These unusual amphibians seem to be oblivious to subzero temperatures.
The frogs don’t freeze totally solid, but two-thirds of their body water turns into ice. If you picked them up, they would not move. If you bent one of their legs, it would break. Inside these frogsicles many physiological changes occur; their heart stops beating, thieir blood no longer flows and their glucose levels sky rocket. “On an organismal level they are essentially dead,” said Don Larson, a graduate student at the University of Alaska. “The individual cells are still functioning, but they have no way to communicate with each other.”
Biologists have known for decades of this phenomena, but they now know that the frogs can freeze longer and tolerate cooler temperatures than previously thought. It is still not fully understood how the frogs thaw and wake up out of their hibernation. “They are actually hard to touch when they’re frozen,” Larson said. The amount of glucose in a single wood frog while in a frozen state is comparable to the amount of glucose found in the blood of a human child. Wood frogs begin their annual deep freeze by digging into the earth, and covering themselves in leaf litter. They thaw themselves in late April and May.
While a few other amphibians and reptiles are known for their ability to withstand extremely low temperatures, the wood frog seem to be unique in its ability to remain in a frozen state and survive far longer than any other known species.