How do Arctic animals survive in subzero temperatures?

The answer

Arctic animals use a remarkable array of cold-survival strategies. The wood frog allows up to 65% of its body water to freeze, surviving with no heartbeat and no brain activity for months by flooding its cells with glucose as a cryoprotectant. Arctic woolly bear caterpillars can freeze and thaw repeatedly over 14 years before completing metamorphosis. Polar bears have black skin under transparent, hollow fur that traps heat, plus a layer of blubber up to 4.5 inches thick. The Arctic ground squirrel supercools its blood to minus 3 degrees Celsius during hibernation without ice crystal formation, reaching the lowest known body temperature of any living mammal.