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It turns out that the iconic “Chicago Rat Hole” is not, in fact, a rat.
In 2024, the cartoonish impression of a rat-looking animal in a slab of concrete in Chicago’s Roscoe Village neighborhood turned into a viral sensation and unlikely pilgrimage site. The hole became so well known that it even caught the attention of researchers, who decided to investigate the matter scientifically. The results are in and potentially shocking—the Chicago Rat Hole was probably made by a squirrel.
“With such remarkable preservation, the ‘Chicago Rat Hole’ was named based on the assumption that the original imprint-maker was an unfortunate brown rat (Rattus norvegicus), a species quite common in urban centres, that met its end soon after a fresh layer of sidewalk concrete was poured,” the team wrote in a study published today in the journal Biology Letters.
I am happy to report the Chicago Rat Hole has been restored!
Story to come via @Suntimes pic.twitter.com/c1boKHNnQS
— @vimiller.bsky.social (@_ViMiller) January 19, 2024
The Chicago Rat Hole—which we should probably start calling the Chicago Squirrel Hole—was around for decades before comedian and writer Winslow Dumaine tweeted about it in early 2024, launching it into stardom. And yet the funny-looking shape in the sidewalk, christened “Splatatouille” by a public naming contest, suddenly attracted tons of visitors who left behind coins, flowers, and even medication, according to the study. A softball team even took the rat on as its mascot.
“While the taxonomic attribution of this imprint is not without validity, considering the commonality of brown rats in the region where the imprint was cast and the overall rodent-like appearance of the impression, no alternative hypothesis testing was conducted to rule out other possibilities,” the researchers added.
As such, the team took it upon themselves to investigate the matter and compared measurements from the impression to eight rodent species. Their research ultimately indicated a 98.67% chance that the “Chicago Rat Hole” was a squirrel, meaning that the softball team is going to have to give their mascot costume a fluffier tail.
The Chicago Department of Transportation removed the impression in April 2024 but clearly knew better than to dispose of it. The City Hall-County Building now hosts the iconic piece of local folklore, and its original spot is marked by a plaque from the Riot Fest Historical Society.
Ultimately, the team hopes that its paper will make scientific exploration feel more inclusive. “While we acknowledge the playful spirit of this investigation, our broader aim is to highlight that scientific inquiry begins with curiosity and observation,” they concluded, “qualities that are not exclusive to professional scientists, but accessible to anyone with an interest in understanding the natural world.”
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