Famous ‘Rat Hole’ of Chicago was actually left by a squirrel

By Dean Murray

A famous Chicago sidewalk impression, known as the ‘Chicago Rat Hole’ or ‘Splatatouille,’ has been revealed by researchers to have been made by a squirrel.

The quirky imprint, long assumed to be the mark of a brown rat trapped in wet concrete, has been the subject of a new study published in Biology Letters.

A picture of it went viral after Chicago-based comedian and writer Winslow Dumaine tweeted about it in January 2024, with the comment "Had to make a pilgrimage to the Chicago Rat Hole."

However, the hole had existed for at least 20 to 30 years, according to locals interviewed at the time.

Researchers used detailed measurements from photographs of the impression, comparing these with museum specimens of eight local rodent species.

Their statistical analysis found a 98.67 percent likelihood that the impression was made by a squirrel, either an eastern grey or fox squirrel, with the eastern grey squirrel being the most probable due to its urban abundance.

The brown rat hypothesis was discounted as the impression’s elongated forelimbs and digits did not match the rat’s morphology.

The researchers suggest the squirrel likely fell from a nearby tree and left the impression as it landed in the concrete.

They wrote: "While it is possible that a brown rat was dropped by a bird of prey, it is far more likely that a squirrel, despite their agility, misjudged a leap or slipped from a branch and fell, leaving the impression.

"This theory is supported by reports from longtime residents in the area, who noted the former presence of a tree near the location of the impression."

The original imprint was removed in April 2024 and is now preserved in Chicago’s City Hall.

The researchers add: "We hope this work—in spite of (or perhaps more specifically, because of) its inherent frivolity—resonates with both the public and the scientific community, demonstrating that scientific inquiry does not need to be confined to laboratories or burdened with impenetrable jargon.

"At its core, science simply requires curiosity and a commitment to understanding the natural world around us."