There are 20,000 species of butterflies in the world, but only several dozen are found on the tundra of the North American Arctic. Many Arctic animals have warm, woolly coats, downy feathers, or thick layers of blubber, and Arctic butterflies appear fragile with their fluttering, delicate wings. Yet the hardy butterflies that live at the top of the world have many clever ways to keep themselves warm in cool summers and endure icy-cold winters...