A second region called the periodic region backs up the impact zone with chitosan, a carbohydrate molecule that forms long chains and makes up part of chitin, the substance in crustacean shells.
The chitosan in a peacock mantis' claw, which lies just beneath the impact zone, is stacked at different orientations, like a ream of paper where every sheet has been angled slightly askew. That makes it tough to crack, as any crack that does form has to change directions in order to continue through the claw.
"What nature has actually done is it's actually built things so that, yes, flaws can happen, but when they do happen they're not going to fail catastrophically," Kisailus said.
Finally, a sharp transition marks the striated region, which runs along the sides of the claw. This region acts like the tape around a boxer's knuckles, Kisailus said, compressing the claw to make cracks less likely.
Other than highlighting some cool crustacean abilities, the findings are already proving fruitful for human engineering. Kisailus and his colleagues are working on materials engineered like these natural hammers that could be used in aerospace engineering, automobiles, military body armor and even sports helmets. An initial design, only under development for six months, survived the first tests without a single bullet penetrating, despite being only 0.4 inches (1 cm) thick, Kisailus said.