Ah, rats! Researchers say some other critter likely created Chicago's 'rat hole' sidewalk landmark

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Ah, rats!

Researchers think they have debunked the origin of Chicago's so-called “rat hole,” one of the Windy City's weirdest local landmarks.

Hold on. The rat hole wasn't what you think. It wasn't some back alley bar that served as a speakeasy for the city's notorious gangster clientele or a tenement stuffed to the brim with junk. It was actually a full-body impression of an unlucky critter that got trapped in wet sidewalk cement in the city's Roscoe Village neighborhood about 20 or 30 years ago. The imprint closely resembles that of a spread-eagled rat, complete with outlines of what appear to be tiny claws, arms and legs and even a tail.

The rat hole went viral early last year after comedian Winslow Dumaine posted a photo of it on X. The post drew curious tourists to the site at all hours, with some leaving coins and other odd objects around the impression as a tribute.

The constant traffic drew complaints from neighbors, though, and in April 2024 someone filled the impression with a substance resembling plaster. City workers eventually removed that slab of sidewalk and took it to the City Hall-County Building. A plaque honoring the rat hole remains at the actual site.

Researchers hailing from the University of Tennessee, New York Institute of Technology College of Osteopathic Medicine and the University of Calgary published a paper Wednesday in the journal Biology Letters that concludes the rat hole was most likely created not by the titular rodent but a squirrel or a muskrat.

The researchers studied online photos of the rat hole and compared measurements of the imprint to museum specimens of animals commonly found in the Chicago area. The presence of arms, legs and a tail excluded birds, snakes, frogs and turtles, shrinking the possibilities to a mammal. The claw outlines further reduced the field to rats, mice, squirrels, chipmunks and muskrats, the study said.

The creature's long forelimbs, third digits and hind paws were too large for a rat but fell into the measurement ranges for Eastern gray squirrels, fox squirrels and muskrats. The most probable suspect is the Eastern gray squirrel given how abundant that creature is in the Chicago area, the study concluded.

Other researchers have theorized that a squirrel created the imprint, the study acknowledged. Cement is typically wet during the day, and rats are nocturnal and the creature didn't leave any tracks, suggesting a squirrel misjudged a leap or slipped from a branch and landed in the wet cement, the study noted.

The imprint didn't show any sign of a bushy tail, but hair often lacks the rigidity to create deep, well-defined impressions, and it would have been surprising to find such an imprint, the study said.

“We therefore propose that the specimen be rechristened the 'Windy City Sidewalk Squirrel' — a name more fitting of its likely origins and more aligned with the evidence at hand," they wrote.