Right now, across much of the Northern Hemisphere, squirrels are doing what they do best: squirreling away seeds and nuts for the approaching winter.
But there’s a lot more about these rodents that you might not realize. So we talked to Richard Thorington, curator of mammals at the Smithsonian Museum of Natural History, who presides over one of the world’s largest collections of the squirrel family, or Sciuridae. In all, the Smithsonian is home to more than 30,000 squirrel specimens.
Thorington started studying squirrels almost 50 years ago as a boy who just wanted to keep the varmints off his bird feeder. Since then, he’s co-authored two books on the subject, Squirrels: The Animal Answer Guide and Squirrels of the World, each of which probes the hidden lives of these seemingly everyday creatures and investigates their myriad roles across ecosystems. (See National Geographic’s squirrel pictures.)
Here are some of Thorington’s surprising squirrel facts:
Squirrels exist in nearly every habitat on Earth.
There are 285 species scattered across the globe, ranging from the half-ounce pygmy tree squirrels of western Africa to the nearly 20-pound (9-kilogram) gray marmots of Kazakhstan.
You’d basically have to venture to the planet’s Poles to escape them. (See video: “World’s Weirdest: Flying Squirrels.”)
Squirrels can help trees.
Take the gray squirrel (Sciurus carolinensis) and its penchant for burying acorns for later use. A single gray squirrel can create several thousand buried caches of food each season, not all of which it can hope to rediscover. This is called scatter hoarding.
“In some cases the burying of nuts is good for the trees,” said Thorington.
“You have squirrels taking the acorns from directly underneath an oak tree and burying them somewhere else. That gives the trees more of a dispersal.”
Squirrels can hurt trees.
In other cases, the relationship between squirrels and trees is less harmonious.
North American red squirrels (Tamiasciurus hudsonicus) and Douglas squirrels (T. douglasii) are seed predators that live almost entirely on the cones of conifer trees. They either eat the seeds immediately or store pine cones by the score in secret larders where the seeds remain moist and have little chance of germinating.
Obviously, this is great for the squirrels, because the preserved food supply allows them to survive the winter. The trees, on the other hand, lose their chance at reproducing.
Interestingly, a study published in 1995 in the International Journal of Organic Evolution showed that the trees may have ways of fighting back. The research revealed that in the Rocky Mountains, where red squirrels were prominent, the cones of limber pine trees had thicker seed coats and more resin.
“This makes it difficult for the squirrels to get between the pine cone’s scales,” said Thorington.
Watch video: “Squirrel vs. Hawk.”
But that’s not all. The researchers also found the cones had fewer seeds than normal and less energy per seed. So not only do the squirrels have to put in more work to access the pine cone’s innards, but they also got less of a reward for doing so.
Squirrels make mushroom jerky.
Perhaps one of the most intriguing things you’ll find in Thorington’s books are the lengths to which some squirrels will go to take advantage of a food source. (Also see “Squirrel Birth Control: To Stop Invasion, Science Gets Seedy.”)
For instance, did you know that some squirrels eat mushrooms? Not only that, but red squirrels will hang fungi out to dry between tree branches so that it keeps better over the winter.
Mushroom jerky is also less likely to infect their larder with insect larvae and nematodes.
Squirrels can “garden”—and know their food sources well.
Gray squirrels have also evolved a few rather impressive storage strategies. Thorington explained that the squirrels can tell the difference between red oak acorns and white oak acorns and store them accordingly.
Whites germinate quickly, almost as soon as they hit the ground, said Thorington, and the squirrels tend to eat them immediately since a germinated acorn loses nutritional value. Conversely, reds don’t germinate until spring, so the squirrels prefer to bury those for winter snacking. (See “No Nuts, No Problem: Squirrels Harvest Maple Syrup.”)
And now for the twist. A 1996 study in the journal Animal Behavior observed some squirrels biting through the embryo of white oak acorns, essentially paralyzing the seed’s ability to sprout. The squirrels then buried the modified white oak acorns as they would have with the reds.
What’s more, the scientists witnessed the squirrels digging up red oak acorns that they didn’t need to eat over the winter, nipping off their embryos, and re-burying the food for later use.
“It’s really interesting,” said Thorington. “If you watch squirrels, they are actually doing so much more than you might anticipate.”
If only humans were half as efficient with our leftovers.