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Scientists crack mystery of shrimp packing such a punch it can split your thumb

Mantis shrimp. (Carlos Puma/University of California at Riverside)

In tropical shallows the world over, a peculiar sort of creature scurries along the sea floor, unassuming except for the fact that it sports one of the most powerful biological appendages known to science — its spring-loaded claws. The mantis shrimp, which typically grows no more than 6 inches in length, is an aggressive, burrowing crustacean that looks a bit like a crayfish dipped in neon spray paint. Fishermen call the animals “thumb-splitters” — at least one man has had a finger amputated after a mantis shrimp strike — and a blow from the crustacean’s truncheon can crack a pane of stock aquarium glass.

The mantis shrimp, only distantly related to the species you would find covered in tempura batter, come in two types, which marine biologists divide into “spearers” or “smashers.” The spearers impale prey with a javelin strike of a pointed claw, whereas the smashers use their fist-like appendages to pop the shells of their food. Smashers, and their shrimply hammers — technically known as dactyl clubs — are of particular interest to researchers because of the blistering blows the animals can deliver.

David Kisailus, who teaches at the University of California at Riverside, is studying the mantis shrimp's fist-like club to develop tougher and stronger materials. (Video: University of California at Riverside)

A mantis punch arrives with the acceleration of a .22-caliber bullet, 50 times faster than a human eye can blink. Underwater, the low pressure bubble left in the wake of the punch collapses upon itself in a burst of light and heat, reaching an estimated 8,500 degrees Fahrenheit. Its super-powered blow and vibrant hues have propelled the critter to internet fame, with humorous paeans cropping up in the Web comic “The Oatmeal” and on YouTube.

Researchers, too, have fallen under the shrimp’s spell. How the mantis shrimp can deliver a blow and not destroy its club in the process has long been a source of scientific intrigue. Within the dactyl club, as scientists at the University of California at Riverside previously discovered, sits a corkscrew pattern of chitin (the stuff of insect shells) and areas spackled with hydroxyapatite (the stuff of human teeth). The shapes of the inner club allow for small breaks, rather than snapping the entire claw.

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Now, in a paper published in the journal Advanced Materials, the UC-Riverside scientists and engineers say they have detected a heretofore unknown natural structure in the outer layer — the critical “impact area” — of the club. Were helmets or body armor to be created following this mantis shrimp template, they say, soldiers and football players could be protected from immense blows.

When viewed under a microscope, the outer layer of the club has what the scientists describe as a herringbone structure. There, fibers of chitin and calcium compounds are arranged in a series of sinusoidal waves. When the shrimp strikes a prey’s shell, the researchers think this herringbone wave buckles, dispersing the impact throughout the club without causing catastrophic damage to the predator.

“The smasher mantis shrimp has evolved this exceptionally strong and impact-resistant dactyl club for one primary purpose — to be able to eat,” David Kisailus, a UC-Riverside chemical engineer and author of the paper, said in a statement.

Based on this research, the scientists have 3-D-printed a prototype helmet that mimics both the inner corkscrew pattern and the outer herringbone layer. “The more we learn about this tiny creature and its multi-layered structural designs,” Kisailus said, “the more we realize how much it can help us as we design better planes, cars, sports equipment and armor.”