The pistol shrimp, a small marine crustacean from the family Alpheidae, is famous for possessing a weapon that rivals the acoustic power of much larger ocean creatures. Measuring only a few centimeters in length, species like Alpheus heterochaelis and Synalpheus pinkfloydi generate an extremely loud, sharp crack. This sound has led to the claim that the snapping shrimp may be the loudest animal relative to its size. The mechanism is a physical phenomenon involving a temporary bubble that releases immense energy.
The Mechanics of the Pistol Shrimp’s Snap
The pistol shrimp’s power comes from one specialized, oversized claw, which it can cock and rapidly close. This swift motion forces a high-speed jet of water out of a plunger-and-socket mechanism, rather than the claw parts hitting each other. The water jet accelerates so rapidly that the pressure drops below the water’s vapor pressure, causing the instantaneous formation of a vacuum-filled cavity known as a cavitation bubble.
The bubble is unstable and immediately collapses with violent force. This implosion generates a powerful shockwave that travels through the water. The collapse is so energetic that it produces an intense flash of light (sonoluminescence) and temperatures reaching over 4,400 degrees Celsius. The resulting shockwave is the primary force used by the shrimp.
Measuring the Pistol Shrimp’s Volume
The instantaneous noise of the collapsing cavitation bubble registers as one of the loudest sounds recorded in the animal kingdom. Peak pressure levels near the source cite the sound at over 210 to 220 decibels (dB re 1 μPa). For perspective, a sustained noise this loud in the air would be destructive, far exceeding a jet engine at takeoff (120 to 150 decibels). The snap is an extremely brief, high-intensity event, not a sustained vocalization.
The physical impact of this shockwave is significant within a small range. The pressure pulse created by the snap can reach a force of 80 kilopascals at about four centimeters from the claw. This force is powerful enough to stun or instantly kill small prey, such as larval fish or smaller crustaceans.
Is It the Loudest Animal
While the pistol shrimp’s snap is astonishingly powerful, it is not the loudest animal overall, but the source of the loudest instantaneous, non-biological sound. Its sound results from a physical process—the cavitation bubble implosion—unlike other contenders that use biological mechanisms. The loudest animal title is often attributed to the Sperm Whale, whose sustained echolocation clicks measure 230 to 236 decibels at the source, significantly higher than the shrimp’s snap.
The Blue Whale generates the loudest sustained low-frequency vocalizations, reaching up to 188 decibels, which travel for hundreds of miles underwater. It is important to note that the decibel scale used for underwater measurements is not directly comparable to the scale used for air. The shrimp’s noise is a singular, explosive event, while the whales produce prolonged, high-acoustic-power communications.
Why the Pistol Shrimp Needs Such a Loud Weapon
The primary function of the shrimp’s powerful snap is to secure food by stunning or killing small prey near its burrow entrance. The shockwave provides a swift and effective hunting method for the crustacean. The snap also serves a role in territorial defense and communication with other shrimp.
When encountering rivals, a shrimp will snap its claw to assert dominance and warn off intruders. In large colonies, the collective, rapid-fire snapping creates a continuous crackling sound known as “shrimp noise.” This constant acoustic background is so pervasive in tropical and subtropical waters that it has historically interfered with military sonar operations.