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A frog’s long winter

January 15, 2017
Nick Buseman - Grundy County Conservation Operation Supervisor , Reinbeck Courier

A frigid 6 degrees outside causes me to wonder how our frogs and toads are surviving these brutal temps; I doubt they are able to locate a hot water spring here in Grundy County. I have to admit I am not an amphibian expert or lover. Probably the only passion for frogs is to use them for catfish bait in late August. Nonetheless I do admire the little creatures and know how important they are to our ecosystem.

I may be the only one out there that has wondered how a delicate frog or toad could ever survive an Iowa winter. Do they have antifreeze flowing through their veins or just a wonder of God's creation? The fact of the matter is that a frog in Iowa merely sleeps the cold months away or hibernates. Aquatic frogs like my favorite the Leopard frog and the American bullfrog spend their winters sleeping on the bottom of Iowa's rivers, lakes and ponds.Unlike the turtle that typically buries itself in the muddy bottoms of these water sources, the aquatic frogs need to be near oxygen rich water. Aquatic frogs are able to absorb oxygen through their skin. Typically they are found just lying on top of the mud or partially buried on the pond floor exposing them to the oxygen rich water they need to survive. As the water temps drop frogs metabolism slows dramatically so it can sleep the winter away. On the bottom of these ponds the frog is still taking up oxygen through its skin. Examining these frogs they act as if they are dead.

You would think that they are bound to freeze to death in these frigid waters, but they don't. Ice crystals do form in a few places such as their body cavity, bladder, and under the skin, but the vital organs contain a high concentration of glucose which prevents them from freezing. A partially frozen frog will actually stop breathing and its heart will stop beating and appear dead. As the frogs hibernaculum warms above freezing the frog begins to thaw and its heart and lungs resume activity and they wake up from the dead. Truly amazing how a fragile-looking aquatic frog can survive months in a subfreezing bathtub, only to awake from this four month nap and in the spring and swim away.

As a trapper I have run across different aquatic frogs just lying on the bottom of a creek motionless and presumed dead, which is not the case. I have actually placed one in my hand and felt their ice cold bodies and find it amazing to know that he will wake up this spring and continue his life. These frigid temperatures would seem to put a lot of stress on our Grundy County wildlife, but they seem to be equipped to survive better than we are.



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