A hefty crayfish nicknamed "Crawzilla," pulled from the mud during a biological survey in Kentucky, has triggered a nationwide hunt for North America's largest crayfish -- and led researchers to suspect the animals may run into a hard biological ceiling on size.
Caitlin Bloomer, a teaching assistant professor at the University of Illinois Urbana-Champaign's College of Agricultural, Consumer and Environmental Sciences, found the specimen and figured she had the biggest crayfish ever documented. A colleague quickly told her he had caught an even bigger one, prompting Bloomer to ask biologists and museum curators around the country to check their own collections for outsized crayfish, according to ScienceDaily, which cited the university's release.
Using calipers to measure preserved specimens, the researchers assembled a list of 20 unusually large crayfish spanning 18 species, drawing six of the top 20 from the Illinois Natural History Survey and four from the Smithsonian's National Museum of Natural History. Crawzilla, a member of the species Lacunicambarus chimera, known as the crawzilla crawdad, measured 77.5 millimeters and made the list as the only burrowing crayfish among the giants, but it did not take the top spot.
That distinction instead went to a Tennessee bottlebrush crayfish housed at West Liberty University in West Virginia, collected in 2011 and measuring 86.6 millimeters -- now the largest North American crayfish on record, according to the study published in the journal Ecology.
The researchers noticed that nearly all of the largest specimens topped out around 80 millimeters in body length, regardless of latitude, oxygen levels or habitat. Bloomer said the pattern suggests crayfish may hit a biological limit, possibly tied to the strength of their exoskeletons or muscle anatomy, though she cautioned the idea remains a hypothesis that needs further testing. "They all seemed to max out around that 80-millimeter mark, but we weren't sure why," Bloomer said, adding that the chance find "sparked a future research direction."