The tiny claws of young shrimp accelerate through the water like a bullet

When it comes to a quick draw, few creatures beat the adult shrimp (Alpheus heterochaelis). They stun passing fish and enemies with a simple click of a spring-loaded claw, which fires a high-velocity jet that rips through the water, creating a vapor-filled bubble (a cavitation bubble) that then bursts, resulting in a devastating shock wave— complete with a sharp popping sound and a subtle flash of light—to weaken their opponent.

“We can’t see the bubble with the naked eye, it happens very quickly, but we can hear when the bubble collapses,” says Jacob Harrison at the Georgia Institute of Technology in the US. The claws of the adult shrimp collide with each other at incredibly fast speeds of up to 30 ms⁻¹ and the whole process is over in less than a millisecond. But at what point in their development do shrimp grow their hairs, when are they able to launch a jet that can tear through the water, and how does their performance compare to that of their parents?

As a graduate student in Sheila Patek’s Duke University lab, Harrison became a surrogate parent to a growing shrimp troupe and discovered that young shrimp are capable of accelerating their upper claws through water as fast as a bullet from a gun and 20 times faster. quickly from their parents. He published his discovery that the claws of a juvenile shrimp are the fastest-accelerating reusable body part in water at Journal of Experimental Biology.

Having collected four egg-bearing female shrimp from the mudflats off Beaufort, North Carolina, USA, Harrison nursed the young shrimp after hatching, watching them grow until they began clipping their claws at about 1 month of age.

“I couldn’t see it, but I started to hear it,” says Harrison, who filmed the young man’s nail strikes under a microscope at 300,000 fps.⁻¹ over a 3 week period to record every detail of the lightning maneuver as the crustaceans matured. “I had to poke them with a toothpick to get them to break,” he laughs. After spinning more than 280 claws, Harrison began painstakingly reconstructing 125 of the maneuvers to calculate the acceleration of the claws as they slammed shut, the amount of energy used and the power required to produce the water jet.

Incredibly, even the tiniest biting shrimp—with claws that were only 1 millimeter long and weighing just 0.03 mg—could occasionally shoot a jet of water creating an explosive cavitation bubble. “I was completely ecstatic. This nibbling shrimp was about a foot long and could move fast enough to burrow through the water,” says Harrison. When he calculated the acceleration of the thin upper claw as it closed on the lower claw, he was surprised to find it reached an acceleration of 580,000 m/s²— as fast as a bullet and ~20 times faster than an adult’s fingernail — while spinning at more than 1,500,000 degrees/second (250,000 rpm).

“It’s the fastest recorded acceleration for a repetitive, underwater motion,” says Harrison, though he explains that Dracula’s ant jaws accelerate faster in air and sting cells from gelatins accelerate faster in water, but are destroyed every time are triggered. .

Harrison then calculated the power required to produce such an impressive burst and arrived at ~65,000,000 W/kg of muscle, far exceeding the 1200 W/kg measured for the most powerful bird flight muscle. Only a catapult, which stores energy and then releases it instantaneously, could produce such an explosive jet of water.

Thus, shrimp develop the ability to close their claws, creating a cavitation bubble, a little more than a month after hatching, achieving astonishingly fast accelerations that far exceed those of their parents. But Harrison suspects that the young need to drop a few voids before they pile up to form cavitation bubbles.

“Juveniles may ‘practice’ their shots,” he suggests, explaining that juveniles may need to lock and load a few times to build up until they are able to reliably release their ballistic water jets.