The fearsome mantis shrimp has many fascinating attributes, most notably its powerful hammer-like rounded claws -- technically known as "raptorial appendages" -- that it uses to crack open the hard shells of its favoured prey (clams and crabs) and to ward off predators. And now it seems they use them as weapons against each other, smacking rivals for prime territory on their tiny shrimp butts should they dare to trespass on an occupied burrow. Just call it Mantis Shrimp Fight Club.
In a new paper in Royal Society Biological Letters, two behavioural ecologists at Duke University describe their investigation into a kind of ritualistic duel over scarce housing that seems typical of mantis shrimp. They put two such creatures of the same sex into a tank, separated by a solid barrier. One shrimp got a cosy burrow (in the form of a small tube) in which to snuggle; the other had no shelter. When the barrier was removed, it was time to throw down, and see which mantis shrimp would prevail.
The researchers found that the crustacean won't immediately jump to violence. First it will wave its big hammer claws at an intruder, attempting to intimidate the other shrimp with its size and (implied) strength. But co-author Patrick Green told Wired that this almost never works. "There was only one contest that we saw out of 34 that didn't escalate to striking."
As Matt Simon writes in Wired:
This is where things get interesting. Instead of punching its sparring partner right in the face, the mantis shrimp will curl its tail forward, allowing its opponent to strike a special plate on their tail called a telson. This acts like a punching bag, dissipating some 70 per cent of the impact energy. Back and forth, back and forth, until one of them gives up and scoots away. Green reckons this isn't about how hard a combatant can punch, but who's able to strike a greater number of times.
Check out a couple of feisty mantis shrimp in action:
Fierce though the mantis shrimp's hammer blows might be, it's got some competition in a close relative: the pistol shrimp, or snapping shrimp. The pistol shrimp boasts an impressive set of asymmetrically sized claws. The larger of the two produces a very loud snapping sound -- so loud that the mantis shrimp ranks with the sperm whale and beluga whale as one of the loudest animals in the sea.
Each snapping sound also produces a powerful shock wave with sufficient oomph to stun or even kill a small fish (the shrimp's typical prey) -- or a menacing mantis shrimp looking for a fight. That shock wave in turn produces collapsing bubbles that emit a barely-visible flash of light. It's a rare natural example of the phenomenon known as sonoluminescence: zap a liquid with sound, create some bubbles, and when those bubbles collapse (as bubbles inevitably do), you get sort bursts of light. I guess you could call it "shrimpoluminescence," and it's one heck of an effective weapon.
So, mantis shrimp versus pistol shrimp: who would win in a cage fight? Discuss.
Green, P.A. and Patek, S.N. (2015) "Contests with deadly weapons: telson sparring in mantis shrimp (Stomatopoda)," Royal Society Biological Letters 11(9).