Frozen Frogs

Birds migrate, bears hibernate, squirrels and chipmunks live off their caches; animals use many adaptations to survive the cold winter months. There is one group of animals that survives the cold in a most miraculous way: by freezing. Indeed, some types of frogs, including three species found in the Finger Lakes Region, do freeze solid when temperatures drop below 32℉. How is it possible that an animal could freeze and then come back to life?

Wood frogs (Rana sylvatica), spring peepers (Pseudacris crucifer), and gray tree frogs (Hyla versicolor) are tree dwellers by summer. These frogs have climber’s feet and without the ability to dig a hole, they hunker down for the winter in the crevices of logs, and under sheltering tree bark or leaf litter. However, temperatures in these spaces will freeze faster than in the mud of a pond or a burrow in the soil where animals such as toads or turtles hide. To prevent death by cold, these amphibians utilize antifreeze.

This antifreeze, which involves the substance glucose, allows ice crystals to form in the body cavity and under the skin but prevents cells and vital organs from freezing. Rather than build up the chemicals they will need to survive the cold as other freezing-tolerant animals do, the chemical process produced in frogs is almost instantaneous with the onset of freezing temperatures. When temperatures drop below freezing, massive levels of glucose are released into the frog’s body – in quantities that would send a human being into a coma or even death. A frog can withstand this sudden change in body chemistry by become relatively metabolically inert. Water is drawn out of the cells, conserving energy and protecting them from ice crystals. Miraculously, the heart stops beating, and the lungs stop breathing. In all senses, the frog is dead.

The glucose that enters the cells will eventually be used for anabolic metabolism when the mostly life-less body can no longer produce oxygen. This keeps the frozen amphibian alive over the long run. Come warmer temperatures, in an act that almost defies science, the organs thaw and resume activity, and the frog hops off to continue with life as usual.

Nature has invented nearly every possible crazy scheme for surviving harsh conditions. The Finger Lakes Region is home to some of the most miraculous displays in species that turn into frogsicles during the winter but revive to be common and populous during the summer.

By Gabrielle L. Wheeler

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