If everyone you’re related to packs a powerful punch, you would be wise to avoid brawling with family members. The mantis shrimp, which sports a club-like appendage tough enough to crack clamshells, ought to follow that advice but doesn’t. These aggressive marine crustaceans, which grow to several centimeters in length, survive repeated body punches from relatives in tussles over territory thanks to highly effective belly armor. By combining microscopy and X-ray analyses with mechanical tests, researchers have determined how the protective organ known as a telson works so effectively (Adv. Funct. Mater. 2019, DOI: 10.1002/adfm.201902238). The findings may lead to new types of lightweight, impact-resistant materials for helmets, sports equipment, and other applications. A research group led by David Kisailus of the University of California, Riverside, compared the telsons of two types of mantis shrimp: more aggressive ones that smash their prey and less aggressive ones that spear their prey. Telsons of both species are composed of mineralized cuticle with exterior ridges and helical, layered internal structures—features that dissipate energy. But the smashers’ telsons are tougher. They are thicker (up to 700 μm versus 100 μm in the spearing type), exhibit a higher degree of mineralization (based on concentrations of calcium and phosphorus), and are more concave, making the smashers’ armor stiffer and better suited to resisting repeated high-energy impacts.