Patek, S.N. and R. L. Caldwell. 2005. Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus. Journal of Experimental Biology 208: 3655-3664.
Journal of Experimental Biology 208: 3655-3664.
Mantis shrimp are renowned for their unusual method of breaking shells with brief, powerful strikes of their raptorial appendages. Due to the extreme speeds of these strikes underwater, cavitation occurs between their appendages and hard-shelled prey. Here we examine the magnitude and relative contribution of the impact and cavitation forces generated by the peacock mantis shrimp Odontodactylus scyllarus. We present the surprising finding that each strike generates two brief, highamplitude force peaks, typically 390–480·s apart. Based on high-speed imaging, force measurements and acoustic analyses, it is evident that the first force peak is caused by the limb’s impact and the second force peak is due to the collapse of cavitation bubbles. Peak limb impact forces range from 400 to 1501·N and peak cavitation forces reach 504·N. Despite their small size, O. scyllarus can generate impact forces thousands of times their body weight. Furthermore, on average, cavitation peak forces are 50% of the limb’s impact force, although cavitation forces may exceed the limb impact forces by up to 280%. The rapid succession of high peak forces used by mantis shrimp suggests that mantis shrimp use a potent combination of cavitation forces and extraordinarily high impact forces to fracture shells. The stomatopod’s hammer is fundamentally different from typical shell-crushing mechanisms such as fish jaws and lobster claws, and may have played an important and as yet unexamined role in the evolution of shell form.
The related video below shows two force peaks are generated during the strike of a single raptorial appendage. This movie clip shows simultaneous high-speed video images and force sensor output, both sampled at 100,000 samples per second. The first force peak is caused by the impact of the mantis shrimp's appendage against the force sensor. The second force peak is caused by the collapse of a cavitation bubble. Following the primary cavitation bubble collapse, the rebound phase of cavitation is visible in the form of a light cloud of cavitation bubbles, which eventually collapse with lower total forces than the first primary bubble collapse.