The Roscoe Village "rat hole"

After almost two years, Chicago's "rat hole" continues to leave an impression on people:

Initially, the origin story of the hole seemed straightforward: a brown rat scurried onto a wet layer of concrete and became trapped. There were no signs of escape, so the rat most likely died and was somehow eventually removed, leaving behind a cavity as the concrete dried. The series of events seemed plausible in Chicago, which was named the country’s “rattiest” city for the 10th year in a row in 2024 by the pest control service Orkin. However, there has been little evidence to tie the rat hole to its eponymous rodent.

A team of researchers recently analyzed the anatomical dimensions of the rat hole to identify the critter that left the sidewalk impression. Their findings, published Wednesday in the journal Biology Letters, reveal that another rodent is responsible for the hole. “We can affirmatively conclude that this imprint was not created by a rat,” said Michael Granatosky, an evolutionary biomechanist at the University of Tennessee, Knoxville.

Statistical analyses revealed that the size and shape of the hole closely aligned with larger-bodied rodents, particularly tree squirrels in the genus Sciurus. The team concluded with nearly a 99 percent likelihood that the rat hole was left by either an eastern grey squirrel or a fox squirrel, both found within Chicago’s city limits.

A squirrel creating the hole is not a complete surprise.

No, and in fact I thought we'd settled this over a year ago. The most likely hypothesis that I've encountered posits that, sometime in 1993 when the concrete was first poured, a raptor startled a squirrel who was either in the then-existent tree above the sidewalk or on the roof of the apartment building next to it. The squirrel decided that down was better than dead (squirrels can fall any distance without harm if they're conscious) and was surprised to discover the wet concrete below. The lack of exit tracks is easily explained either by the squirrel not having enough mass to make further impressions in the concrete, or the aforementioned raptor plucking the confused, now-stuck rodent up into the air.

In any event, the squirrel has been dead for at least 25 years, the hypothetical hawk probably just as long, and the concrete square containing the impression has buggered off to City Hall.

On the plus side, I think we just found the next winners of the Ig Nobel Prize in biology.