Mantis shrimp didn't evolve armor just to protect themselves from predators. Some of their biggest enemies are fellow shrimp eager to oust them from their burrows. During these attacks, the aggressor uses its hammerlike claw to whack the hard tail plate of the defender with a force thousands of times its own body weight. Good body armor has two options in these situations: rebound the energy onto the attacker, like a trampoline, or dissipate it, like a punching bag. To figure out which strategy the crustaceans adopt, researchers dropped a small steel ball onto the bodies of 17 dead mantis shrimp. When steel met skeleton, almost 70% of the energy was lost—making the punching bag model the winner, the researchers report today in the Journal of Experimental Biology. Things could be different in the water, where the shrimp attack up to 50% faster. But since the shrimp's claws are also smaller than the steel balls used in the experiment, the researchers figure the energy exchange is probably about the same.
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