Any animal with a body part called a “raptorial appendage” should probably be taken seriously. Most mantis shrimp (Neogonodactylus bredini) never grow to more than a few inches long, but their rounded claws strike so fast they can deliver shockwave-producing blows that crack apart hard-shelled prey like clams and crabs. A new study reveals the shrimp even use this weapon on each other. To set up some conflict, researchers placed two mantis shrimp of the same sex, separated by an opaque barrier, into a small tank. One shrimp was provided with a small tube that simulated a nesting site, whereas the other was given no place to live. Scientists then removed the barrier. Thirty-three out of 34 of these contests escalated to striking with the raptorial appendages. The scientists originally suspected that the combatant able to deliver the hardest blow would come out on top, but maximum strike force didn’t correlate very well with success. Instead, landing a higher number of strikes correlated better with victory, the researchers report online today in Biology Letters. The finding could mean the sparring events are ritualistic contests of stamina, rather than an attempt to kill. When being struck by a competitor, shrimp almost always received the blows on a region of their tail known as the telson. As seen in the video above, the shrimp appear to be adopting a specific “telson coil” posture designed to shield themselves from their opponent’s strikes.