Frogs Can Freeze and Thaw Alive

While freezing solid is a death sentence for most animals, the wood frog has mastered a form of natural cryopreservation. This remarkable adaptation is necessary for its survival in the harsh northern climates of North America, where it cannot burrow deep enough to escape the frost line. Instead of fighting the cold, it embraces it, entering a state of suspended animation where it appears clinically dead. This allows it to pass the winter just beneath the leaf litter on the forest floor, encased in ice.

The secret to this incredible feat lies in a biological antifreeze. As ice crystals begin to form on its skin, a signal triggers the frog's liver to convert stored glycogen into massive quantities of glucose. This sugar floods the frog's cells, creating a thick, syrupy fluid that resists freezing, much like antifreeze protects a car's engine. While ice forms in the body cavities and between the cells, the vital organs and individual cells themselves are protected from being shredded by ice crystals. When the weather warms, the frog's heart is one of the first things to thaw, pumping the sugary blood to the rest of its body and bringing the amphibian back to life.