Frogs that live in cold regions can't be active year round. When the weather gets cold their bodies cool down and they can't move.
As the temperature drops, frogs burrow a little ways under forest leaves (so they won't freeze to death), and go into hibernation until the weather gets warm again.
When the temperatures start to drop, Wood Frogs will go buries itself and then shuts itself down. As the temperatures get harsher, the frogs create glucose in their liver by breaking down glycogen using enzymes. This glucose goes out into their body organs and is distributed throughout the bloodstream.
The Wood Frogs are one of serveral species that have the amazing ability to completely freeze solid! (Peepers can do the same...except that in their case they have lots of glycerol, not glucose, in their system)
Since there's so much glucose in the Wood Frog's system, their organs don't get damaged because the sugar in their blood acts as anti-freeze. They can stay completely frozen like that for 2 weeks or more. They stay frozen for as long as the temperature of the ground is below freezing. They have no choice. They are the exact temperature of the environment they are in. When they thaw out, it's like an icecube coming to life!
The first thing that happens when they thaw is the heart starts beating again. Then they start gulping air and shaking out their limbs. Finally, the when the frog is fully recovered, he can hop away!
Why is this important? Just think what it could mean for people if we could develope drugs that do the same thing for humans! "Needs a heart transplant? No hearts available?? Okay, give him 500cc's of froggie coolaid and throw him in the cooler!"
And you'd never guess what the first thing these frogs want to do when they thaw out is!
No, not breakfast - they go find the nearest breeding ponds!! In fact, these guys are known as very explosive breeders.
The term "explosive" refers to the duration of their breeding activity. The woodfrog breeds only for a few short nights, sometimes only one night! This is contrast to the breeding duration of say the Green Frog (R. Clamitans) whose breeding season is 2-3 months!
(I guess that would explain why they'd be in such a hurry to get to that breeding pond)
Nor are these guys particluarly picky! ANY pool of water will do (Even if it's not completely thawed water yet or if its just a puddle!)
(Wood frog photo used with permission. Copyright ©Lenny Flank.)
For more information on the Wood Frog see these links: