A giant crayfish nicknamed "Crawzilla" has sparked an unexpected scientific discovery, revealing a possible biological limit to how large North America's crayfish can grow.

The investigation began when Caitlin Bloomer pulled an enormous Crawzilla crawdad from the mud during a biological survey in Kentucky. Crawzilla is the creature's actual common name, and Bloomer was convinced she had captured the largest crayfish ever documented. But when she proudly showed her discovery to a colleague, the reaction was not quite what she expected.

"I thought, 'There's no doubt I have caught the biggest crayfish anyone's ever seen!' I brought it back to campus to show my colleague, naturally bragging about having caught the biggest-ever crayfish.…