Most people know very little about groundhogs, which is kind of weird considering how obsessed we become with the little fur-balls every Feb. 2.
Think about it: What other animal inspires more than 20,000 people to embark on a pilgrimage to a small Pennsylvania town and hold an all-night vigil, through biting wind and snow, just so they can witness the animal’s emergence from hibernation? What other creature can depend on news outlets (like this one!) to devote whole segments and articles to the weather prowess of one of its kind — in this case, a marmot named Punxsutawney Phil?
When you look at it that way, Groundhog Day is more than a little bizarre. (Am I right or am I right or am I right?)
So in an effort to add a little biology to the boondoggle, we’re going to get to know the world’s most famous ground squirrel. That’s right, groundhogs are technically rodents of the squirrel family and the tribe Marmotini, but you may know them as woodchucks and whistle pigs.
If you’re unfamiliar with the modern meteorological predictions made by the marmot, the theory goes like this: If Phil sees his shadow, we will have six more weeks of winter. The tradition is scientifically bonkers, of course, but it’s rooted in something tangible. Before they immigrated to Punxsutawney, German farmers would start planting their crops when hedgehogs started to emerge from hibernation. When they got to America and found no hedgehogs, they subbed groundhogs into the game.
Strange as the festival may seem — a bunch of guys in top hats yanking a whistle pig out of a fake burrow — it’s actually sort of perfect, if you know a little bit about hibernation.
Hibernation is critical to a groundhog’s existence, said Kenneth Armitage, a population biologist and professor emeritus at the University of Kansas. It allows marmots to live in extreme environments, places where food disappears for several months of the year. Hibernation dictates when marmots can reproduce, whether they’re social and how they act when they’re not hibernating.
Lots of animals hibernate, of course, and it can look different from species to species. But marmots hibernate like a boss. For instance, hibernating bears can sustain body temperature losses of only a few degrees, while groundhogs allow their bodies to sink to temperatures just above freezing. Their hearts, which normally beat at about 85 to 90 beats a minute, switch into slow motion, beating maybe three times in the same interval. Their torpor is so extreme, in fact, that they nearly stop consuming oxygen.
Groundhogs can remain in this suspended animation for four to five months, waking only to shiver up some heat every 10 days or so if their body temperatures get too close to freezing, Armitage said. When spring approaches, the groundhog will assess the world around it and determine whether it’s time to get up and feed or dip back into another hibernation bout. It’s this “arousal cycle” that the Groundhog Day celebration mimics.
But here’s the thing about male groundhogs whose living conditions are more natural than Phil’s: They don’t just poke out their heads to see if the sun is shining. They’re looking for love.
“Marmots have to get reproduction going as soon as they can,” said Armitage, who spent 41 years studying the critters at the Rocky Mountain Biological Laboratory. “We have documented that females that reproduce relatively late in the spring, they themselves have low survivorship, and their young have very, very low survivorship.”
Do it or die, in other words.
Unfortunately for Phil, his body can’t produce sperm while he’s hibernating, so woodchuck males must wake up earlier than females. It’s believed that the males of all 15 marmot species spend a few quiet days in their burrows, just daydreaming and cranking out swimmers, before they emerge.
Speaking of groundhog spermatogenesis: Phil’s testes spend most of the year hidden up in his body cavity and only rappel down for the breeding season. This is one reason it can sometimes be extremely difficult to determine a groundhog’s gender. Another is that the penis is what Armitage calls “pretty obscured.” (If you are really dying to tell a girl from a boy, you’ll need to whip out your tape measure and mark the distance between a groundhog’s anal and genital openings. A male’s perineum is, on average, at least two times longer than a female’s.)
Here’s another fun fact about groundhogs: They have eight nipples, while every other species of marmot has 10. This may be because groundhogs, Marmota monax, are the original marmot — the most ancient of the 15 known species worldwide, said Armitage. Unlike the others, they’re short on nipples and social skills — literally, a marmot apart. Groundhogs are the only solitary marmot.
There are plenty more fascinating aspects of groundhog life. For instance, whistle pigs can climb trees. Their burrows have toilet chambers. And in the 1970s, scientists mailed a bunch of groundhogs to Australia to see whether they could shift their circannual rhythm by six months. (They did!)
You see, there’s so much more to groundhogs than shadows and superstitions! And the best part is, you didn’t even have to relive the same day a hundred times to break the cycle and achieve marmot enlightenment.