June 7, 2012 | 6
The psychedelic-looking peacock mantis shrimp (Odontodactylus scyllarus) has a decidedly non-peacenik way of getting a meal: clubbing it.
This small (3 to 18-centimeter-long), solitary stomatopod wields two dastardly hammer-like appendages. At just 5 millimeters wide, each dactyl club can generate a force of 500 Newtons. That’s enough punch to shatter the glass of a standard home aquarium. But more to the shrimp’s interests, it can smash into the shells of gastropods and other well-protected prey, allowing it to grab some escargot to go.
But how does this crazy crustacean’s club inflict such punishing blows thousands of times without damaging itself? A new study, published online June 7 in Science, examines the inner hardware of this impressive weapon.
The club features multiple layers of mineralized hard and shock-absorbing materials, according to the researchers, led by James Weaver, of the Wyss Institute for Biologically Inspired Engineering at Harvard University. If the club does sustain a small fracture, it is unlikely to spread thanks to the jagged structure of its chitosan fibers, which run at cross-angles.
“The insights gained from natural materials such as those described may find applications in armor plating,” K. Elizabeth Tanner, of the University of Glasgow’s School of Engineering, wrote in an essay in the same issue of Science. The shrimp’s club suggests some small structural elements could make a big difference. “Designers of armor could use the models of the nanoscale composites to optimize the impact resistance,” she wrote.
And history shows that humans had been using a similar, if less high-tech, approach at least as far back as Ancient Roman times. Like the crisscrossing fibers of the mantis club, Roman shields were made so that “layers of wood were combined such that the grain direction alternated between vertical and horizontal, and were joined together with glue,” Tanner wrote. “The resulting shield containing alternating stiff and compliant layers, resembling those found in the periodic and striated regions of the dactyl club,” she noted.
The shrimp’s impressive abilities hardly stop with the composition of its club. The speed of its blows, which can accelerate to some 23 meters per second, create cavitation bubbles, which increase the force of impact on the target (such as “mollusk shells, crab exoskeletons, the skulls of small fish and the occasional weary fisherman,” the researchers noted). These arthropods are also outfitted with some of the most awesome vision hardware in the animal kingdom. Instead of being equipped with three color-sensing pigments like we are, they have a dozen. Talk about trippy.