Wood frogs have adapted to super cold climates by freezing over the winter. During this time, they stop breathing and their hearts cease to beat. They produce a special antifreeze substance that prevents ice from freezing within their cells, which would be deadly. Ice does form, however, in the spaces between the cells. When the weather warms, the frogs thaw and begin feeding and mating again. Wood frogs are one of the first frogs to begin the breeding season.