A groundhog is a stocky, burrowing rodent about the size of a house cat, with brown fur, short legs, and a bushy tail. Groundhogs are also called woodchucks or whistle-pigs (because of the sharp whistling sound they make when alarmed). They live throughout much of North America, digging elaborate underground burrows with multiple chambers and exits.

Groundhogs are famous for two things: eating and sleeping. During spring and summer, they devour enormous amounts of plants, vegetables, and crops, sometimes frustrating gardeners. But in fall, they retreat to their burrows and hibernate through winter, their body temperature dropping dramatically as they survive on stored fat. When they emerge in early spring, they're among the first animals to signal that winter is ending.

This emergence inspired Groundhog Day, a tradition where people watch to see if a groundhog sees its shadow on February 2. According to folklore, if the groundhog sees its shadow, there will be six more weeks of winter; if not, spring will arrive early. The most famous groundhog weatherman is Punxsutawney Phil in Pennsylvania, though his predictions aren't exactly reliable. The tradition is more about celebrating the promise of spring than actual meteorology.