Invertebrates
Pistol Shrimp
Alpheidae · also called pistol shrimp, snapping shrimp
The pistol shrimp is a few centimetres long and one of the loudest animals in the ocean. It hunts by cocking an oversized claw and snapping it shut fast enough to fire a bubble — a bubble that flashes with light and, for an instant, reaches a temperature close to the surface of the sun.
Overview
Pistol shrimp — family Alpheidae, over 600 species — live in warm and temperate shallow seas worldwide, on reefs, seagrass, oyster beds, mangroves, and rubble. Most are only 3–5 centimetres long. One claw is dramatically enlarged into the “pistol”; the other is a normal small claw.
The snap
The shrimp cocks the pistol claw open against a latch, loads the muscle, and releases. The claw slams shut in under a millisecond, ejecting a water jet at about 100 km/h. The water moves so fast that it vaporises into a bubble, and when that bubble collapses it produces:
- a loud bang (up to ~210 decibels at source)
- a tiny flash of light (sonoluminescence)
- a heat spike estimated near 4,700 °C at the centre — briefly, microscopically
The shockwave of the collapsing bubble stuns or kills prey without the claw touching it, from up to a body length away.
An ocean of crackle
Where snapping shrimp are dense, the sound of countless snaps merges into a constant crackling roar — the dominant natural noise in many shallow seas. Submarines in WWII hid in shrimp beds to mask their sound from sonar, and the crackle still interferes with underwater acoustics today.
The goby partnership
Many pistol shrimp share a burrow with a goby fish: the near-blind shrimp digs and maintains the tunnel, the sharp-eyed goby stands guard and signals danger with a tail flick against the shrimp’s antenna. Both get a safe home neither could build alone.
Status
Pistol shrimp have not been assessed for conservation and are, collectively, abundant across the world’s warm coasts.
Pistol Shrimp: common questions
How does the pistol shrimp's snap work?
One claw is enlarged into a pistol-like structure with a hammer part and a socket part. The shrimp cocks the hammer open, held by a latch and building tension in the muscle, then releases it. The hammer slams into the socket so fast that it forces out a jet of water at around 100 km/h. Moving that quickly, the water pressure drops enough to vaporise it, creating a short-lived bubble (a cavitation bubble). When the surrounding pressure crushes that bubble a fraction of a millisecond later, the collapse releases a loud bang, a tiny flash of light, and a spike of heat that has been estimated at nearly 4,700°C at the centre — briefly comparable to the surface of the sun, though in a microscopic volume for a microscopic instant.
What does it use the snap for?
Mainly hunting and defence. The shockwave from the collapsing bubble can stun or kill a small fish, worm, or crab without the claw ever touching it, from up to a body length away, and the shrimp then drags the prey into its burrow. The snap is also used to warn off or fight rival shrimp and to deter predators, and in some species to communicate. A few pistol shrimp species have taken it further and live socially in sponges with a single reproductive queen, the only known eusocial marine animals.
Why are pistol shrimp such a problem for navies and sonar?
In warm shallow seas, snapping shrimp are so numerous that the combined sound of countless individual snaps produces a continuous crackling roar — often described as sounding like frying bacon or burning twigs — that is one of the dominant sources of natural underwater noise. During the Second World War, submarines learned to hide in shrimp beds because the noise masked their own sounds from enemy sonar and hydrophones, and pistol shrimp crackle still complicates sonar operation and marine acoustic research today.
What is the deal with the shrimp-and-goby partnership?
Many pistol shrimp species live in a mutualistic pair with a goby fish, sharing one burrow in the sand. The shrimp is an excellent digger but has very poor eyesight, so it handles the construction and constant maintenance of the tunnel. The goby has good vision but cannot dig, so it acts as a lookout, sitting at the burrow entrance while the shrimp works with one antenna kept in contact with the fish's body. If the goby spots a predator it flicks its tail against the antenna, and both animals dart into the burrow. Each partner gets a safe home it could not have alone.