A rat-shaped hole in a Chicago sidewalk went viral early last year, with scores of people heading to the hole with coins and other offerings. However, a new study suggests that the so-called “Chicago rat hole” was not actually made by a rat, but was likely the imprint of a squirrel.
By comparing the characteristics of the burrow with information about local rodent populations, the researchers determined that the impression was most likely made by a squirrel. The study was published on Wednesday (October 15) in the journal Letters in Biology.
The hole, a well-preserved imprint of a rodent's death in damp concrete, existed for decades before going viral. It became a tourist attraction in 2024 after Chicago artist and comedian Winslow Dumaine. published about its existence on social platform X.
Had to make a pilgrimage to the Chicago Rathole pic.twitter.com/g4P44nvJ1fJanuary 6, 2024
“Squirrels are much more TV-ready than rats,” Dumaine told Live Science. “But I think the fact that it was nicknamed Rathole played a key role in why it became popular.”
When researchers came across photos of the hole on social media, some thought it didn't look like a “super rat,” says the study's senior author. Edwin Dickinsonarchaeologist from the University of Calgary, told Live Science. It also seemed unlikely that a rat could make such a cast on wet concrete without leaving a trail leading to it. These suspicions prompted researchers to analyze the hole more deeply.
Using the citizen science app iNaturalist, which catalogs local fauna, the study authors identified possible animals that may have made the hole. From the deepening they realized that it must be an animal with four legs, five claws and a tail.
Back then it was all a matter of proportion. The study authors had no way to measure the hole itself, which city officials fixed in April 2024, citing unrest that crowds caused in the Roscoe Village neighborhood. However, they were able to get the exact dimensions thanks to many photographs of the print that people posted next to coins and other objects.
The researchers compared their measurements with samples from the American Museum of Natural History. Statistical analysis of these data showed with a probability of 98.7% that the hole was made by either an eastern gray squirrel (Skriur Karolinsky) or fox (Sciurus niger) .
In light of this discovery, scientists proposed renaming the rat hole “Windy City Sidewalk Squirrel” to better represent its origins.
The authors hope the study will help people see the joy of science.
“The rat hole may be a medium, but the message we hope to perpetuate in this study is that … there is nothing too difficult or scary about following the scientific method,” Dickinson said. “It’s something we can all use in our lives.”
