by Dr Jonathan D Sarfati

The mantis shrimp (aka stomatopod), has one of the strongest ‘punches’ in nature. A specimen only an inch (2.5 cm) long can draw blood if they hit a human finger, and bigger ones have caused severe injuries. Considering how some can grow a foot (30 cm) long, and one has even reached 15 inches (38 cm) long, they are not to be messed with! 13

With an intricate catapult mechanism, its ‘fist’ (called a dactyl) can accelerate up to 10,600 g1(a greater acceleration than a 22-caliber bullet—while underwater—and hundreds of times what humans can stand2), high enough to induce a mini-explosion called cavitation.3 If kept in captivity, this punch can shatter the glass walls of their tanks. And in the wild, it breaks the shells of its prey, which are often marvels of engineering toughness in their own right.4

We also noted its amazing colour vision, with 12 primary colours receptors—four times as many as humans.5 Later we noted how DVD makers wanted to copy the shrimp eye’s ability to change the polarization over multiple colours.6

But back to its powerful punch: it raises the question of how the ‘fist’ itself can survive. We noted that it moults frequently to regenerate. But frequent moulting could not be the whole story. It could not be frequent enough to withstand 50,000 high-speed strikes against hard prey shells in its lifetime.

Recently, a research team at the University of California, Riverside, discovered what makes its club so damage-resistant.7

There are actually three different regions of the club that cooperate “to create a structure tougher than many engineered ceramics.”8

The outer region that actually contacts the prey is mineral rich, like our bones. But this intrinsically brittle material is buttressed by the next layer, comprising “highly organized and rotated layers of chitin … fibers dispersed in mineral”. (Chitin is a complex polymer, i.e. made from smaller molecules joined together, in this case modified sugars. It is the main component of the outer “skeleton” of many invertebrates, and we have used it to make a strong biodegradable material called “shrilk”.9) In the mantis shrimp club, the arrangement of its tough chitin fibres enables them to absorb the energy of stress waves from the impacts. And the third region comprises “oriented chitin fibers, which wrap around the club,” which holds it together….

 

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