“Crawzilla” was huge. Then scientists found an even bigger crayfish

A nationwide search for giant crayfish uncovered a record-breaking Tennessee specimen and a surprising mystery about how big these freshwater creatures can grow. Scientists found that North American crayfish seem to hit a biological size limit, possibly because of their muscles or protective shells. “Crawzilla” was huge. Then scientists found an even bigger crayfish.

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. But, as all biologists and sport fishermen do, he took one look and said, ‘No way, I’ve caught bigger,’" said Bloomer, a teaching assistant professor in the Department of Natural Resources and Environmental Sciences within the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois Urbana-Champaign.