The rat of the famed Chicago Rat Hole was almost certainly a squirrel

The Chicago Rat Hole was the city’s hottest new attraction last year. Tourists swarmed to a quiet residential neighborhood to see the decades-old imprint of a rodent pressed into sidewalk concrete. They lined up around the block at all hours to take photos. Pilgrims brought offerings: rat figurines, cheese, money and Malört. One guy proposed.

In the end, the Chicago Rat Hole was so popular that city officials tore out the concrete slab that housed it, hiding away something so beloved it had become a nuisance.

It turns out, all of it - the adoration, the infatuation, the worship - was based on a mistake.

Scientists say they have all but proved there was no rat involved in creating the Chicago Rat Hole. On Wednesday, researchers published an article in the peer-reviewed journal Biology Letters stating there’s about a 98 percent chance it was a squirrel that fell into wet cement. Their work puts to rest decades of speculation and myriad theories about the unfortunate critter who, in an inauspicious moment lost to time, fell from above and splatted into wet cement.

“It completely excluded the brown rat,” Michael Granatosky, a biology professor at the University of Tennessee at Knoxville, said Wednesday in an interview.

Watching the viral moment from afar, Granatosky was impressed by accounts of admirers’ curiosity and well-reasoned theories about the Chicago Rat Hole’s origin, which he described as a “really powerful use of the scientific method.” He set out to prove whether a rat was the source as a way to show science can be fun and accessible.

“It’s important to just find some joy occasionally,” he said.

Granatosky and his team started with a long list of suspects: virtually every animal in Chicago. They excluded large swaths of the animal kingdom: species that don’t have four similar limbs (birds and snakes) or tails (toads and frogs), quickly concluding their culprit was one of about three dozen mammals found in Chicago.

From there, they ruled out rarities (feral hogs, Mongolian jirds) and animals that are too big to make a rat-size imprint, including deer, dogs, cats and beavers.

The imprint animal’s most distinctive combination of features - five claws on its hind paw with only four on the front and a relatively small “thumb” - let researchers narrow the field to eight species, including the brown rat, eastern chipmunk, muskrat and several types of squirrels.

Unable to access the imprint itself, Granatosky and his team scoured the internet to find 25 clear images that included known objects like coins that allowed them to determine scale. They measured the length of six body parts, resulting in 75 “virtual specimens.” They searched museums to collect and measure the same body parts on physical specimens, allowing for the fact that they didn’t know the animal’s age or sex. They fed the data into a computer, and using statistical analysis software, compared measurements and determined the probability of each species.

The result: The rat of the famed Chicago Rat Hole was almost certainly a squirrel. Although they demurred at definitively identifying a culprit, researchers listed their top three suspects: the Eastern gray squirrel, fox squirrel and muskrat.

Granatosky’s research lends academic weight to a theory that’s been floating around Chicago’s Roscoe Village neighborhood for years. Days after the Chicago Rat Hole achieved viral fame, Cindy Nelson, who has lived across the street for nearly 30 years, said she had long suspected it was a squirrel. A “huge, old, beautiful” oak towered over the hole for years, but the tree eventually got sick, she said. After it was cut down, passersby examining the impression would look up at nothing but sky and grow visibly confused, a sentiment she understood.

“It’s impossible for a rat to jump straight up - vertical - and drop in the middle,” she said Wednesday.

The scientists noted the former tree in their study as evidence of their squirrel theory. They cited previous research examining squirrel skeletons that revealed the creatures fall from trees routinely.

“This risk is particularly pronounced for Eastern grey squirrels in urban centres, which are approximately 4.5 times more likely to have healed injuries compared to their rural counterparts,” they wrote.

Armed with their findings, Granatosky and his team are pushing for the landmark to be renamed to something more accurate. In their paper, they suggested the “Windy City Sidewalk Squirrel,” although in an interview, Granatosky conceded that it’s not as catchy as the original.

“It just doesn’t have the same flow,” he said. Granatosky also noted that Chicagoans still call the city’s tallest building “Sears Tower” even though it was renamed “Willis Tower” 16 years ago.

Winslow Dumaine, the artist and card game designer whose post on X in January 2024 brought viral fame to a few square inches of Chicago sidewalk, cackled at the suggestion of a new name for the animal imprint. There are several reasons the suggestion won’t stick, he said: One, no one in Chicago refers to their home as “the Windy City.” Two: The original has had nearly two years to ingrain itself in people’s brains. Three: It just sounds cooler.

The Chicago Rat Hole isn’t about the creature that made the indent; it’s about the meaning people ascribe to it, Dumaine said. A rat is gritty, has an edge and survives, even if others are trying to kill it - all concepts that Chicagoans identify with.

“It doesn’t matter what rodent it was,” Dumaine added. “Marilyn Monroe wasn’t her real name, and she captured the hearts of the nation. The Chicago Rat Hole doesn’t need to be made by a rat to do the same thing.”