PATEK, Sheila N.; CALDWELL, Roy L.; Univ. of California, Berkeley; Univ. of California, Berkeley: Snail smashing forces of the peacock mantis shrimp

Peacock mantis shrimp (Odontodactylus scyllarus) use a specialized pair of forelimbs, the raptorial appendages, to smash open snail shells. The appendages accelerate to extreme speeds within milliseconds, producing high impact forces as well as cavitation between the limb and the strike surface. The power amplification necessary to achieve such extreme movements is generated through the use of a spring-loaded click mechanism. In this study, we measured strike impact forces using a three-axis piezo-electronic load cell. The surface geometry of the load cell was varied to include either a flat surface or a curved surface with a radius of curvature similar to that of a typical snail shell. Mantis shrimp readily strike food-scented objects, thus strikes were elicited by dabbing shrimp paste on the load cell surface. We examined the scaling of forces relative to body size, the magnitude of impact forces on curved versus flat surfaces, and the relative magnitude of the three recorded force vectors. We also compared the forces due to limb impact to the forces generated by the implosive collapse of cavitation bubbles. Animals ranging in size from 11-15 cm body length generated average strike forces in the Z-axis (perpendicular to the plane of the load cell) of 391 N on the flat surface, and 416 N on the curved surface. The maximum recorded Z-axis forces scaled with body size across individuals and ranged from 330-1314 N. An average of 75% and 77% of the impact force was directed into the load cell (Z-axis) in flat and curved surfaces, respectively, with the remainder of the force distributed approximately evenly between the two other axes (X and Y). One surprising result was that peacock mantis shrimp generated impact forces of over 16kN/kg body mass (or over 1700 times their body weight).