When a sea creature evolves its front limbs into firearms, it is hardly surprising that it goes a little crazy.

In the ocean there is a peculiar kind of animal that comes with its own "firearm":the pistol shrimp- and the name really is apt. The family Alpheidae (snapping shrimp) contains several hundred species, and their most obvious feature is a pair of asymmetrical claws. The one that is disproportionately large is their deadly weapon: it can use a bubble as a "bullet" to stun or even kill enemies or prey. The sound produced by this deadly strike can reach 210 decibels, far louder than an actual gunshot (which averages about 150 decibels). For this reason, the pistol shrimp is also known as the snapping shrimp or the popping shrimp.

It is fair to say that the pistol shrimp is one of the most powerful and also one of the noisiest creatures on Earth, but it is also very fragile. Pistol shrimp can form alliances with many kinds of animals, and can even form peculiar colonial living arrangements to protect themselves from undersea predators.

The most distinctive feature of the family Alpheidae is that the two claws are not the same size; the larger claw can snap shut with such force that it can momentarily heat the surrounding water to nearly 4500 degrees Celsius.

A one-of-a-kind trick

The pistol shrimp has two claws, one large and one small, and the large claw can grow to half the length of the shrimp's body. Unlike the small claw, which is symmetrical and works like a pair of tongs, part of the large claw is immobile and contains a cavity; the other part of the large claw has a movable "piston" that fits exactly into the cavity. The muscles of this "giant claw" are strong and powerful, and when the "piston" closes, the jet of water squeezed out of the cavity can reach a speed of 32 meters per second. This speed is so great that it can create a pressure lower than the saturated vapor pressure. Under such low pressure, tiny bubbles form in the water, and when the pressure rises again, the bubbles burst. This phenomenon is called cavitation.

In essence, it is the bubbles bursting that produce the loud clicking sound, not the impact of the large claw itself. More importantly, at the instant the bubbles burst, the temperature of the surrounding water can reach an astonishing nearly 4500 degrees Celsius, almost as high as the surface temperature of the Sun. The resulting shock wave can be used to attack prey such as small fish and small crabs. For these small animals, dying immediately is actually a stroke of luck. After hitting its target, the pistol shrimp drags the prey back to its burrow and eats it. Sometimes the pistol shrimp even uses cavitation to drill holes in basalt rocks.

The high-speed water jet can reach 60 miles per hour,

Armed with this powerful "bubble weapon," the pistol shrimp is anything but low-key. In the habitats where they gather, pistol shrimp often "fire" at one another or hunt, so sonar equipment frequently picks up a crackling noise like burning branches. When swimming in tropical regions, if you listen carefully, you will very likely hear this sound around you. Some people think that rather than regarding these pistol shrimp sounds as noise interfering with sonar, it is better to take a different angle and listen carefully to what is happening underwater, using the sounds of pistol shrimp and other animals to assess the health of coral reefs.

Like many crustaceans, the pistol shrimp will shed its claw when attacked. However, this does not make the noise disappear for long. Although the structure of the large claw looks somewhat complex, the pistol shrimp will still regrow one - in a peculiar way.

What regrows on a pistol shrimp that has lost its large claw is not a large claw, but a small claw. Most interestingly, after the next molt of the exoskeleton, the original small claw begins to grow more and more like a large claw, and eventually grows into a large claw with the same powerful killing force. In other words, the pistol shrimp has essentially switched its weapon to the other hand.

Regeneration of a lost limb sometimes goes wrong. If a pistol shrimp loses its small claw, it will occasionally mistakenly grow a large claw, ending up with two large claws. "Dual pistols" may sound impressive, but in fact the pistol shrimp still needs the small claw to help it feed. The large claw is like a gun for hunting, while the small claw is the knife and fork for eating meat.

Some species of pistol shrimp choose to live on sponges

In a study of one species of pistol shrimp (scientific name Alpheus heterochaelis), scientists at the University of Twente in the Netherlands used a high-speed camera to discover a peculiar "shrimpoluminescence." Because the bubble produced by the pistol shrimp is compressed extremely rapidly, the heat cannot dissipate, so the temperature inside the bubble can reach over 4700 degrees Celsius and produce a flash of light lasting only a few hundred-millionths of a second. The duration is so short that the human eye cannot see it. This was the first discovery of an animal using this method to produce light.

Social animals

The pistol shrimp is actually an easy animal to get along with - if you have what it needs. Although many species form a monogamous living arrangement, many other species have mastered the essence of symbiotic relationships and formed close alliances with other marine life. For example, corals provide shelter for pistol shrimp, and in return, the pistol shrimp uses its bubble weapon to attack the tube feet of sea stars, driving away these echinoderms that feed on coral polyps. Some pistol shrimp seek shelter among the tentacles of sea anemones, just like the familiar clownfish.

Another kind of pistol shrimp digs burrows in the sand and then invites gobies to come and live there. They often linger together at the burrow entrance, looking for prey while staying alert for predators. The goby can provide the pistol shrimp with early warning. In many cases, the pistol shrimp will keep at least one antenna touching the goby's body, and if the goby flees into the burrow, the pistol shrimp will follow right behind. On the other hand, the pistol shrimp is a diligent digger, constantly excavating the burrow and keeping it clean.

The pistol shrimp forms a partnership with the goby, and they live together in the same burrow.

Among all the symbiotic relationships of pistol shrimp species, the most incredible are those species that have formed social organizations. Hundreds of pistol shrimp live inside a sponge, and this form of social organization is called "eusociality." These pistol shrimp are ruled by a larger "shrimp king" and "shrimp queen," the only pair of pistol shrimp able to reproduce.

"Among the millions of marine species, only a few species of pistol shrimp can do this, which is truly remarkable," said Emmett Duffy, a marine biologist at the Smithsonian Institution. "But even more remarkable, these pistol shrimp are ecologically very similar to some social insects (think ants and bees)." Emmett Duffy was the first biologist to describe these social phenomena in pistol shrimp.

These pistol shrimp are very small, about the size of a grain of rice. They feed on anything that falls onto the sponge, as well as tissue shed by the sponge itself. In this respect, they are most similar to termites, which also build nests in wood and feed on wood fibers.

These antennae enable the pistol shrimp to sense the bubble shock waves of its own kind. In fact, when two pistol shrimp quarrel, they keep enough distance that both can "fire" at each other without either causing fatal injury.

Within a colony, the smaller juvenile individuals surround the "shrimp queen" in the middle of the sponge, and it has been observed that larger individuals react more aggressively, actively defending when intruders appear. When a single pistol shrimp encounters an intruder, it rhythmically emits a "click-click-click" sound to summon its companions. The pistol shrimp that come to help also launch attacks in sync, clicking at the same time.

This is a warning signal to outsiders: you have entered a sponge inhabited by a colony of pistol shrimp. In other words, if you insist on forcing your way in, then it will not be just a few pistol shrimp, but the entire colony joining forces to kill you.

The key point is that this little guy is cheap, on average 30 yuan each

According to fish keepers who have raised them, at night the aquarium keeps making

"gaba gaba gaba gaba" sounds, which is quite interesting

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