The potent mechanics of the mantis shrimp's predatory strikes

Mantis shrimp (Stomatopoda) use a specialized pair of forelimbs, the raptorial appendages, to capture prey. Peacock mantis shrimp (Odontodactylus scyllarus) smash open snails and consume the contents as their primary source of food. High speed video images, recorded at 5000 frames per second, reveal that peacock mantis shrimp forelimbs reach maximum speeds from 12-23 m/s (in water!).

While recording these images, we noticed cavitation bubbles forming between the limb and the snail. As a result of the limb's extraordinary speed, the water cavitates (vaporizes) when the limb strikes the prey. Cavitation is a destructive phenomenon; when these vapor bubbles collapse, they essentially cause a small implosion in the water which produces heat, light and sound. For example, rapidly rotating boat propellers are often badly damaged by cavitation to the point of developing holes in the metal.

Such extreme speeds in water require substantial energy storage and release. Energetic calculations show that these movements cannot be controlled by muscle contractions alone. In other words, the mantis shrimp needs a potent power amplification system in its limb. Earlier studies showed that mantis shrimp have latches which hold the limb in place until the animal is ready to strike. More recently, we have demonstrated that mantis shrimp use a 4-bar linkage mechanism coupled with exoskeletal springs and latches to power this remarkably forceful strike.

Images and video clips

Here a peacock mantis shrimp smashes a snail (regular speed video). Filmed at 5000 frames per second, and played back at around 30 frames per second (slowed down 333x), the formation of a cavitation bubble can be seen between the limb and the striking surface. Filmed at 20000 frames per second, and played back at 30 frames per second, cavitation is visible as the limb strikes a snail.

A peacock mantis shrimp (Odontodactylus scyllarus) strikes a force sensor. Filmed at 100,000 frames per second in color, this movie clip shows the mantis shrimp's dactyl heel striking a force sensor. The formation and collapse of cavitation bubbles are visible between the sensor's surface and the mantis shrimp's appendage.
Synchronous high-speed video and force output of a peacock mantis shrimp's strike.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.

In the image below, cavitation is visible between the limb and a snail (indicated by black arrow).

Publications (see "Publications" page for links):

• Patek, S.N., B. N. Nowroozi, J. E. Baio, R. L. Caldwell and A. P. Summers. 2007. Linkage mechanics and power amplification of the mantis shrimp's raptorial strike. Journal of Experimental Biology 210: 3677-3688.
• 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.
• Patek, S.N., W.L. Korff and R.L. Caldwell. 2004. Deadly strike mechanism of a mantis shrimp. Nature 428: 819-820 and supplementary online material.

Selected Press Links:

• Science Matters@Berkeley: The Toughest Shrimp Around
• Natural History magazine Biomechanics column by Adam Summers
• Lurker's guide to stomatopods