Building Better Armor: Lessons from Combat Shrimp

Mantis shrimp, or stomatopods, are the planet’s most powerful bare-knuckle boxers, armed with dactyl clubs that literally fly faster than a speeding .22 caliber bullet. Each strike boils the surrounding water and creates a tiny cavitation bubble, which then implodes with a sonic pop that can render targets unconscious. Consider that: if the strike itself doesn’t get you, its aftershock will. And that’s just the variety of stomatopod equipped with blunt fists -  others launch their lance-like arms to pierce prey.

These little lobster cousins, usually between 4 and 12 inches long, are capable of beating their way through the hard shells of armored animals, such as crabs and clams. That so small an animal can crack shells, split fishermen’s thumbs, and fracture aquarium glass is an extraordinary mechanical feat in its own right.

But there’s another seldom-explored angle to these underwater pugilists: how can a bare fist survive ballistic-level impacts? Put another way, how does the mantis shrimp fire the same armor-piercing bullet 50,000 times?

Peacock Mantis Shrimp

This peacock mantis shrimp shows off its durable weapons, the two oval-shaped hammers at the end of its arms. Photo by Silke Baron.

A team of researchers from several institutions investigated the remarkable composition, mechanics, and effective durability of what they called a “biological hammer” - the results are detailed in a new study published in the journal Science

"Nature spends thousands of years trying out a variety of solutions to a problem, and only the best solutions survive," said Brookhaven Lab physicist and study coauthor Kenneth Evans-Lutterodt. "We wanted to understand how Nature managed to build such an incredibly robust structure that is still lightweight."

Ultra-bright x-rays from Brookhaven Lab’s National Synchrotron Light Source probed the mineral composition of the dense mantis shrimp clubs. The results revealed a multi-tiered structure that uniquely combines two crystal forms of the hard mineral hydroxyapatite (found in human bones and teeth) with shock absorption from flexible chitin (a complex sugar) fibers.

"That detailed information was then input by other collaborators into precise mechanical simulations that helped demonstrate how the structure remains intact in the face of the huge stresses that the club undergoes," Evans-Lutterodt said. As it turns out, the structure allows for tiny fissures and cracks to open up within the hammers, preventing the kind of rigidity that might lead to more substantial fractures.

Proposed applications for this Nature-tech include developing lighter materials for airplanes, electric cars, and military body armor.

More info can be found at the Brookhaven Lab press release. The research paper, published online June 8, includes details on electron density mapping, x-ray diffraction imaging, exterior structural analysis, and more about the full collaboration.

It’s also worth reading the Wikipedia page on stomatopods. In addition to the mantis-fist combat style, they also have the world’s most advanced eyes, often mate for life, and come in dazzling peacock patterns.

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Gives the word "shrimp" a whole new meaning.

Don't search for mantis shrimp on youtube if you are squeamish. Seems there is a cult of mantis shrimp videos on youtube of the cockfight variety.

The mantis shrimp also holds the record for the animal that can see the widest range of the electromagnetic spectrum (from infrared to UV). I have a hard time understanding why they would have evolved this capability. Are they such efficient predators that they can spend resources on developing this visual capability? Does their hunting environment and strategy need this capability? It seems strange for one animal to have two very extreme adaptations.

It may be that one of those adaptations developed first, and it then opened the door for the second. Such extreme vision facilitated hunting, which in turn encouraged their bullet-quick fists to develop - or vice versa. Here are a few theories from Wikipedia: recognizing types of coral, transparent prey, shimmery predators such as barracuda; the punch speed demands unparalleled depth perception and rapid adjustments; and they actively fluoresce during mating rituals with signals tied to specific wavelengths.

Here's a quote from a 2008 study covered in Wired, which also points out that they uniquely use circular polarized light to communicate with each other: "One idea is that the more complicated your sensory structure is, the simpler your brain can be," said Cronin. "If you can deal with analysis at the receptor level, you don’t have to deal with that in the brain itself."

To more efficiently hunt, to really take advantage of that weaponry, maybe they evolved that amazing and perhaps excessive sensory structure.