The groundhog, or woodchuck, is one of 14 species of marmots, a subgroup of the squirrel family. One of the largest members, groundhogs live a feast-or-famine lifestyle: they gorge themselves all summer to build up plentiful reserves of fat, then retreat to their underground burrows to snooze through the winter while drawing their sustenance from body fat. During hibernation, the animal’s heart rate plunges, and its body temperature is not much warmer than the temperature inside its burrow.

Groundhog hibernation gave rise to the popular U.S. custom of Groundhog Day, held on February 2 every year. Tradition dictates that if a groundhog comes out of its burrow and sees its shadow, there will