During the cold winters, the Alaskan Wood Frog becomes a frog-shaped block of ice until the spring.
Each September, the wood frogs of Alaska do a very strange thing: They freeze. They do not freeze totally solid, but they do freeze mostly solid. Two-thirds of their body water turns to ice. If you picked them up, they would not move. If you bent one of their legs, it would break.
Inside these frozen frogs other weird physiological things are going on. Their hearts stop beating, their blood no longer flows and their glucose levels skyrocket.
“On an organismal level they are essentially dead,” said Don Larson, a graduate student at the University of Alaska, Fairbanks who studies frogs. “The individual cells are still functioning, but they have no way to communicate with each other.”
The craziest thing of all may be that in this frozen state, they can withstand temperatures as low as zero degrees Fahrenheit for as long as seven months, and then, when spring arrives, thaw out and hop away.
Biologists have known for decades that some frogs freeze in the winter and thaw in the spring, but a paper published in the Journal of Experimental Biology reports that they can freeze longer and tolerate cooler temperatures than previously thought.