The American Bullfrog and his various amphibious friends are some of the great unexpected pleasures of pond ownership. The question many pond owners find themselves wondering, though, is where they go in winter, and how they survive the freezing cold.
Frogs are true cold-blooded animals, unable to internally unable to regulate their body temperature. Generally, when they’re cold they seek out sunlight, and when they’re hot they seek out shade or water. But what do they do in winter, when it’s far too cold for the sun to keep their temperature up, even below freezing? Well, like many animals, especially cold-blooded ones, they hibernate. Many more terrestrial frogs dig holes on land or find tight crevices in which to hide. Aquatic frogs, like the Bullfrog, are more comfortable in water. Contrary to what many pond-owners believe, they don’t dig deep into the mud at the bottom of a pond like some turtles do. Frogs require more oxygen than that allows, even when hibernating. Thus, bullfrogs mostly just sink to the bottom of the water, and will even occasionally swim very slowly around to get more oxygen from the water.
Perhaps the coolest (sorry) thing about frog hibernation, though, is how they survive actual freezing temperatures. In the lead-up to the hibernation period, frogs will add excess glucose (sugars) to their vital organs. This glucose works pretty much just like the antifreeze in your car, lowering the freezing temperature of the water in their cells enough that the organs aren’t damaged by temperatures well below the freezing point of water. Thus, some frogs can even survive being frozen into a solid block of ice and come out the other side just fine when it warms!