It’s mid-December and we’re inside keeping warm, while temperatures outside are below freezing (in parts of the northern hemisphere, that is). But what about our amphibian friends? How do they survive the winter? After all, they would seem vulnerable to temperature extremes with their thin skins and need to constantly stay moist.
Actually, we don’t need to worry about the frogs. They are well-equipped to deal with the cold weather, even with Arctic temperatures.
In the fall, frogs first need to find a place to make their winter home, a living space called a hibernaculum, that will protect them from weather extremes and from predators. The frog then “sleeps” away the winter by slowing down its metabolism. When spring arrives, it wakes up and leaves the hibernaculum, ready for mating and eating.
Aquatic frogs and toads such as the leopard frog and American bullfrog usually hibernate underwater. They don’t, however, dig into the mud like turtles—turtles are able to slow down their metabolism in a much more extreme way than frogs and can get by with almost no oxygen. Aquatic frogs need more oxygen—they lie just above the mud, or only partially buried in the mud, so they are near the oxygen-rich water. They may even occasionally slowly swim around.
Terrestrial frogs and toads typically hibernate on land. Those frogs and toads that are good diggers like the American toads burrow deep into the soil, safely below the frost line. Some frogs, such as the wood frog and the spring peeper, aren’t good diggers and so must scout out their winter homes in deep cracks and crevices in logs or rocks, or they might dig down into the leaf litter.
Yet these frozen frogs aren’t dead—they have a kind of natural anti-freeze in their bodies. Ice crystals form in their organs and body cavity, but a high concentration of glucose in the frog’s vital organs prevents freezing. A partially frozen frog will stop breathing: its heart will stop beating and it will seem dead. When spring approaches and their hibernaculum warms up above freezing, the frog’s frozen body will thaw, and it will come back to life.
As you go about your holiday, all bundled up for the cold, think of the frogs with their amazing adaptations for survival, safe in their winter homes, waiting for spring.
Here’s a video from YouTube about the hibernation of a wood frog. It’s pretty amazing—take a look!
Most of the information from this post came from an article in Scientific American, How Do Frogs Survive the Winter? Why Don’t They Freeze to Death? by Rick Emmer.