Why gray squirrels and black walnuts go together so well

For many years, we’ve been finding black walnut bits on the benches surrounding our campfire circle. I know where the walnuts come from and I know gray squirrels are eating them. Why squirrels like to eat them on elevated platforms is puzzling. Let’s review.

The squirrel

The moniker of gray squirrel is something of a misnomer. These rodents are more than just gray. The body fur is gray and white underneath and a mixture of brown, gray, and yellow on top while the bushy tail is actually gray frosted with white. In winter, this squirrel’s coat features conspicuous white tufts at the back of their ears. A black variety of gray squirrel exists as well.

Black squirrels are black regardless of the season. Melanistic is the term zoologists use to describe dark forms of a particular species. Melanistic gray squirrels can be sighted as individuals, as they are here at Stillman, or as colonies. As early as 1856, Illinois naturalist Robert Kennicott reported on a colony of fifty black squirrels that had been shot along the Rock River.

The walnut

If you’re a squirrel looking for nuts to eat at Stillman Nature Center, the most plentiful option are black walnuts (Juglans nigra).

Walnut trees have large pinnately (featherlike) compound leaf made up of 15 to 23 leaflets. Each leaflet can be up to 1.5 inches wide and 3.5 inches long. Put 15 to 23 of those together and you’ve got one big leaf! The walnut fruit itself measures between 1.5 and 2.5 inches in diameter. For comparison, a billiard ball is 2.5 inches in diameter.

Walnuts do not fall from a tree ready to crack open. No, they are covered with a light green, aromatic, somewhat roughened husk. The aroma is distinctive and anything but subtle. Dig your fingernail into that green hull and you will be rewarded with a refreshing mix of citrus and spice. Be advised that the husk contains a brown dye that can stain your hand and other surfaces such as our benches.

Inside the husk and a protective shell that requires cracking, is the tasty kernel that most people, especially those who cook, are familiar with. Be aware that many walnuts used in the kitchen are English walnuts (Juglans regia) that are grown in this country but are indigenous to southeastern Europe and Asia.

In addition to producing desirable fruit, black walnut is a valuable timber tree. It is a favorite of furniture makers. Its value was not lost on early colonists. As early as 1610, black walnut was being exported from Virginia back to England.

Squirrels meet nuts

One of the reasons we have a good crop of walnuts at Stillman Nature Center is thanks to the efforts of one our first dedicated volunteers, Roger Laegeler. Besides cutting buckthorn, Roger would occasionally bring along bags of walnuts to distribute along our trail. It wasn’t long before our resident squirrels began taking advantage of his largesse and, in the process, eating and distributing the nuts on their own.

When it comes to black walnuts, squirrels exhibit a clear interest in these nuts probably due to their high fat and protein content. These nutrients are essential for energy storage, particularly during the winter. Fats also support healthy brain function and provide insulation. The dense caloric content of black walnuts makes them an exceptionally beneficial food for squirrels to store and gobble up.

Gray squirrels are essentially eating machines. They eat roughly five pounds of seeds and nuts per week. They will also consume mushrooms, flowers, buds, and berries. Keeping in mind that the average weight for adult gray squirrels is 1.25 pounds, they are eating more than their entire body weight every week!

This time of year, squirrels are not only eating to survive; they also need energy for breeding and raising young. Gray squirrels breed once or twice a year with the first season beginning in late January or February and the second in late June or early July. A litter of three to five young will arrive in the nest by the middle of March. Interestingly, one of the first things a young squirrel does when it leaves the nest is bury nuts. So how do they open these aromatic green billiard balls?

That a squirrel can actually grab hold of a sizable walnut is somewhat surprising. Their strong incisor teeth allow squirrels to bite through tough substances like walnut husks and shells. By creating a small hole for leverage, their teeth can be used to break open walnuts Alternatively, the shell can be dropped from a great height onto the ground. Thanks to their eight molars, squirrels can easily grind up the nut. But why do it on our campfire benches? The answer remains a mystery.

Not long ago, another squirrel-related mystery made national news.

CSI: Chicago

At the beginning of 2024, Chicago’s Rat Hole (aka “Splatatouille”) was all over social media.

To many, it appeared an unfortunate rat had somehow landed and died in some wet cement on a North Side sidewalk. There were no footprints or actual remains to be seen. The rodent’s impression solidified and attracted many visitors who left tributes such as candles, coins and even plastic rats. Not everybody agreed that this fossilized splat was made by a rat.

Researchers from the University of Tennessee-Knoxville decided to study the hole. This was somewhat challenging since the hole had been filled in and then re-excavated. There was, however, ample photo evidence of the original depression with nearby offerings to provide scale.

Their findings? According to Dr. Michael Granatosky, “We can affirmatively conclude that this imprint was not made by a rat.” His team decided that there was a 99% chance that the “rat hole” was left by either an eastern gray squirrel or a fox squirrel. Not surprisingly, the hairs on a squirrel’s bushy tail lacked the heft to leave an impression. Of course, the imprint of a nearby walnut or acorn would certainly have added something to the identification speculation. I can’t help but wonder if there was a walnut tree nearby.

Be that as it may, I think the last words should go to Roald Dahl, author of “Charlie and the Chocolate Factory,” “Nobody except squirrels can get walnuts whole out of walnut shells every time.”

• Mark Spreyer is executive director of the Stillman Nature Center in Barrington. Email him at stillmangho@gmail.com.