You’ve heard the story. Every February 2nd, the groundhog peeks out from his burrow. If he sees his shadow, we’re in for six more weeks of winter. If he doesn’t, spring will come early. True story? Not likely. Truth is, most groundhogs celebrate their holiday curled up asleep in underground burrows.

All summer long, groundhogs stuff their furry faces with as many plants as they can eat. When autumn comes and temperatures drop, chubby groundhogs waddle into their burrows and curl up for a long winter’s nap. Groundhogs, like chipmunks, ground squirrels and several bats, hibernate during winter. Animals that hibernate go into a deep sleep. How deep?

During hibernation, a groundhog’s temperature drops from 96 to about 45 degrees. (If your temperature dropped that much, you’d never wake up.) While hibernating, a groundhog’s heart beats only four or five times a minute, and it breathes only once every four minutes. In this slowed-down state, groundhogs live off their fat and go without eating or drinking for nearly five months.

Why do groundhogs hibernate? Groundhogs are vegetarians—they eat only plants. In winter, most plants disappear, leaving hungry groundhogs with little to eat. So, instead of staying awake to look for food, groundhogs sleep. By mid-February, plants begin greening Missouri’s hillsides, and skinny groundhogs awaken with growling tummies. By then, it won’t matter if the groundhog sees his shadow. He’ll know for sure that spring will soon be here.