Crab Fight

It’s not pretty when male fiddler crabs engage in a claw-snapping brawl during mating season. 

They wave their big claws outside their burrows to woo females. Those with bigger claws – and those who wave them faster – tend to get the girl. 

Scientists have long observed this phenomenon. But what they didn’t understand was how these crustaceans – known for their oversized claws – adjust their flashy claw-waving displays in the face of competition. 

“We know many animals adjust their sexual displays if rivals are nearby, but less is known about how they react to the actual displays themselves,” Joe Wilde, lead author of a new study, explained in a statement. 

For their study, Wilde and his colleagues from the University of Exeter in the United Kingdom developed a 3D-printed, Bluetooth-controlled robot crab nicknamed “Wavy Dave” and sent him to the mudflats of Portugal’s Ria Formosa Natural Park to mingle with male fiddler crabs during mating season. 

Wavy Dave was set up roughly a foot from the burrows of male crabs, while cameras recorded the interaction between the crabs and the robot.  

When the robot waved, real males waved for longer and were less likely to retreat – especially when Dave’s claw was small. But when the bot sported a larger claw, most males backed off, possibly to avoid a fight they’d likely lose. 

While the crustaceans initially seemed wary, however, they quickly puffed up when the ladies complained about Wavy Dave. 

“The females realized he was a bit odd, and some of the males tried to fight him,” said Wilde. “One male broke Wavy Dave by pulling off his claw. We had to abandon that trial and reboot the robot.” 

The findings showed that the crabs tailor their behavior to the perceived level of competition, offering new insight into how subtle and strategic animal courtship can be, according to Futurism. 

“Our findings reveal the subtle ways in which these crabs adjust their behavior to compete in a dynamic environment, investing more in signaling when it is likely to be most profitable,” added Wilde.