Engineering excellence: mantis shrimps register shell shape and target the weakest part
The crustaceans position their prey, then rain hundreds of blows on its most vulnerable section. Tanya Loos reports.
Mantis shrimps, from the genus Stomatopoda, are famed for the impact force of their tiny club-shaped claws. The speed with which the two halves of a claw come together is the fastest movement of any known animal. One might be forgiven, therefore, for thinking that the crustacean dispatches its mollusc prey with single super-powered strike to crack its shell.
But surprising new research on the hunting behaviour of the mantis shrimp reveals that far from utilising a brute strength one-punch attack, it hits prey shells repeatedly, tens to hundreds of times, targeting very specific locations depending on the species.
The biomechanics of the “lightweight high-acceleration hammers” are well known, but until now the behavioural strategies underpinning mantis shrimp foraging had not been studied. Rachel Crane from Stanford University in California, US, along with a team of fellow researchers, housed the shrimps in tanks, and presented them with a several molluscs, including the round shelled Nerita versicolour and the long, helical shelled Cerithium atratum.
First results were disappointing.
“We have endless hours of video footage of mantis shrimps doing pretty much everything besides eating,” Crane says.
After a while, however, the team captured the animals in the act. Crane and her colleagues were surprised to see the shrimps carefully manipulate prey into position, and then deliver as many as 460 blows on a specific spot on the shell.
In round shells, the shrimps moved the snails so they could attack the opening. In helical shells, the target was the apex.
To test which parts of the shell are vulnerable, the researchers created a tiny robot – known as the Ninjabot – that struck with the acceleration and force of a real mantis shrimp. Ninjabot testing revealed that the shrimps targeted the weakest point of the shell – meaning that, at present, the shrimps are slightly ahead in the evolutionary arms race between predator and prey.
The research is published in the Journal of Experimental Biology.