The mantis shrimp, Odontodactylus scyllarus, is a large predatory shrimp that smashes its prey to pieces. Camouflage isn’t really a strong point though.This colorful crustacean uses its ‘dactyl club’ to break open clam shells. Probably because they don’t spot it coming. Seeing as the US army have become interested in recent biomimetic research on the material of clam shells for use as body armor, that’s a hell of a punch.
The mantis shrimps club relies on multiple layers of fine chitin fibers, each of which is offset by a few degrees of rotation to the one below it. This hellicoidal enables it to withstand multiple impacts without failure. Kisailus and his research team mimicked this arrangement of chitin with carbon fire composites and tested it against the same material with the fibers in each layers running perpendicularly at 90 degrees to the other. The hellicoidal carbon fiber, in layers which were offset at 7.8 degrees, 16.3 degrees and 25.7 degrees, had dents that were 49% shallower than the normal carbon fiber arranged at 90 degrees. They also had 15-20% more strength after the test than the traditional design. The shrimp researchers though did highlight that this structure enabled the cracks to propagate between the layers and dissipate the energy of the blow to prevent the material breaking fully. This is very similar to the process of twinning that makes clam shells so strong.