The Feisty Shrimp That Kills With Bullets Made of Bubbles

This is what it looks like when a pistol shrimp gets stung by a bee. I jest, of course. Everyone knows that bees can’t swim. That giant claw is perfectly natural: The shrimp uses it to snap so hard that it briefly heats the water to 8,000 degrees Fahrenheit.

The greatest, smoothest gunslinger of all time—and I say it knowing full well I’m going to get emails for this opinion—is Clint Eastwood’s Man With No Name, aka Blondie, of Sergio Leone’s classic spaghetti westerns. I mean, at a public hanging the guy sat back and sniped the rope to free the accused, then blasted off the hats of the men in attendance. Because let’s be real: Wearing a hat to an execution is bad form.

But the greatest real-life gunslingers have to be the pistol shrimp, aka the snapping shrimp, hundreds of species with an enormous claw they use to fire bullets of bubbles at foes, knocking them out cold or even killing them. The resulting sound is an incredible 210 decibels, far louder than an actual gunshot, which averages around 150.

Pound for pound, pistol shrimp are some of the most powerful, most raucous critters on Earth. Yet at the same time they are quite vulnerable, allying with all manner of creatures and even forming bizarre societies to protect themselves from the many menaces of the ocean bottom.

The Life Despotic

The pistol shrimp has two claws, a small pincer and an enormous snapper. The snapper, which can grow to up to half the length of the shrimp’s body, does not have two symmetrical halves like the pincer. Instead, half of it is immobile, called a propus, which has a socket. The other half, called a dactyl, is the mobile part. It has a plunger that fits into this socket. The shrimp opens the dactyl by co-contracting both an opener and closer muscle. This builds tension until another closer muscle contracts, setting the whole thing off with incredible force.

“Mama Said Knock You Out” is the anthem of the pistol shrimp, which most of the critters, having never met their mothers, feel somewhat conflicted about.

When the plunger slams into this socket it displaces water that jets out at 105 feet a second, a velocity so high that its pressure drops below the vapor pressure of water. Tiny bubbles already present in the water suddenly swell in this low pressure, then collapse when the pressure climbs again.

“You essentially create this cavitation bubble,” said coral reef biologist Nancy Knowlton of the Smithsonian Institute. “And when the bubble collapses, it generates that snap sound,” as opposed to the impact of the claws themselves making the noise.

More importantly, the collapse of the bubble generates, for a split second, temperatures of 8,000 degrees Fahrenheit, nearly as hot as the surface of the sun, and also, oddly, a flash of light. The resulting shockwave bombards the shrimp’s prey, which if it’s lucky will die instantly because it’s then dragged into the pistol shrimp’s burrow and consumed. That’s not so fun if you’re half-conscious (see the awesome BBC video below). It’s such a powerful blast that some species use it to drill into solid basalt rock, snap after snap, to make a comfy little home, like an aquatic version of Dig Dug, only with fewer dragons, or whatever those things are.

Some species of snapping shrimp take up residence in sponges for protection. I love the expression on this little one’s face more than almost everything.

The creature has weaponized bubbles. (Another ocean critter, the mantis shrimp, produces cavitation bubbles when it rapidly strikes prey with its clubs, though it’s unclear if it evolved to use the bubbles or if they’re just a welcome destructive side effect). And pistol shrimp are far from conservative with their snapping. In fact, vast colonies of them all firing off at each other or their prey have been known to disrupt sonar equipment with a cacophony likened to the crackling of burning twigs. Yet there is an upside to all the racket.

“Anywhere you go swimming in the tropics, if you listen around you, you can hear these things,” said Knowlton. “And some people have argued that instead of thinking about snapping shrimp sounds as an obstacle to hearing what it is you’re trying to hear, you can also use the sounds of snapping shrimp and other things on coral reefs to assess the health of the reefs.” Lots of noise means lots of life (and lots of pissed off sonar operators).

Like many crustaceans, the pistol shrimp will willingly shed its claws if attacked, because it’s better to lose a pincer than your life, but that won’t stop the noise for long. As complicated a structure as its snapping claw is, the shrimp will grow another—in a surprising way.

Relieve a pistol shrimp of its snapping claw and it’ll grow back not another snapper, but a pincer like its remaining claw. But what’s the fun in having two pincers? After the next molting of its exoskeleton, the original pincer starts looking more and more like a snapper, eventually growing to the full size and strength of the lost pistol. The shrimp has switched weapon hands, modifying the existing pincer to more quickly get back into fighting shape.

Things can glitch, though, and a pistol shrimp can end up with two pistols if it loses a pincer and it grows back as the wrong type, according to Knowlton. Dual-wielding snappers sounds awesome, sure, but they need pincers to dig into the stunned prey once they’ve gotten them back into the burrow. Think of the claws as complementary forks and knives … knives that actually are more like guns. OK think of them as forks and guns.

Social Security

For all their orneriness, pistol shrimp are really quite easy to get along with—if you have something to offer them. While many species pair into monogamous lifetime bonds, others have mastered the art of symbiotic relationships, teaming up with all manner of other sea critters. Taking shelter in the three-dimensional maze that is coral, for instance, a shrimp in turn dutifully attacks the giant, voracious crown-of-thorns starfish that come to feed on its host, blasting the fiend’s tube feet to drive it away. Others take shelter in the stinging tentacles of sea anemones, just like the famous clownfish.

Pistol shrimp will pair up with gobies to live in and protect a single burrow. It’s a friendship that at any moment could be undone by the shrimp accidentally snapping the goby in the face and knocking it unconscious. Not unlike most friendships, really.

Another species will dig a sandy burrow and invite a goby over. The lovely new couple will hover at the entrance on the lookout for both prey and predator. “The goby provides advance warning to the shrimp,” said Knowlton. “And in many cases [the shrimp] puts its long antennae, one of them at least, on top of the goby. So if the goby runs back into the burrow, the shrimp withdraws as well.” In exchange, the pistol shrimp, a quite accomplished digger, constantly excavates the burrow to keep it tidy.

But most incredible of all symbiotic snapping shrimp relationships are the handful of species that actually form societies of hundreds of individuals inside sponges, an extremely advanced level of organization known as eusociality. The shrimp are ruled by a larger queen and king, the only ones who breed, surrounded by their doting subjects.

“It’s remarkable in the sense that of all the millions of species in the ocean, a few species of snapping shrimp are the only marine animals that do this,” said marine biologist Emmett Duffy of the Smithsonian Institution, who was the first to describe these societies. “But what in some ways is more remarkable is how similar these things are ecologically to some of the social insects.” Think ant and bee colonies that we know so well, only wetter.

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