The Shrimp Whose Punch Boils the Water

The mantis shrimp is not a large animal, but it strikes like something far bigger. Some species, known as smashers, carry a pair of heavy, club-like appendages folded beneath their bodies, which they use to hammer open hard-shelled prey. In the spring of 2003, researchers at the University of California, Berkeley, filmed one of these strikes properly for the first time, and what they recorded was so fast that it has been described as perhaps the swiftest kick in the animal kingdom.

The species they studied was the peacock mantis shrimp. According to UC Berkeley, its strike reaches peak speeds of 23 metres per second, with peak accelerations of between 6,300 and 8,000 times the force of gravity. National Geographic later reported accelerations of up to 10,000 times the force of gravity. The blow itself delivers a force of well over a hundred times the shrimp’s own body weight, which is why a mantis shrimp can crack shells that seem far too tough for a creature of its size.

Capturing it on film took special equipment. UC Berkeley reports that the team, led by the biologist Sheila Patek, used a high-speed camera rented through a BBC film crew that could record 5,000 frames per second. The findings were published in the journal Nature. The footage revealed the secret of the strike’s power: a saddle-shaped structure in the striking limb that works as a spring, storing up energy and then releasing it all at once.

The water is where things get stranger still. National Geographic explains that the club moves so quickly that it lowers the pressure of the water in front of it, causing the water to boil. This releases small bubbles, which collapse when the water pressure returns to normal, unleashing tremendous amounts of energy. The process is called cavitation. According to UC Berkeley, these exploding bubbles contribute to the destruction of the shell, generate sound and perhaps even light.

That light turned out to be real. National Geographic reports that Patek’s cameras revealed small flashes of light as each strike made impact. So a mantis shrimp breaking into its dinner is producing a tiny underwater light show at the same time. As for the dinner itself, National Geographic notes that large smashers can make meals of crabs, buckling their thick armour as easily as they can damage aquarium glass, which is one reason the animals are famous among aquarium keepers.

So the next time you see a picture of a brightly coloured mantis shrimp, remember what is folded beneath it: a spring-loaded hammer fast enough to make the sea boil around it. It is one of nature’s most extraordinary pieces of engineering, carried by an animal small enough to hide in a crack in the reef. And every time it strikes, it lights up the water, just for an instant, to open a shell for lunch.