The pistol shrimp's claw snaps a bubble that flashes light and stuns fish
A shrimp only 3 to 5 centimetres long rivals sperm whales and belugas for the title of loudest animal in the sea. Its oversized claw snaps shut so fast it blows a collapsing bubble that can kill small fish, briefly emits light, and in large colonies can confuse naval sonar.
The snapping, or pistol, shrimp family numbers about 1,119 species worldwide, most of them burrowers on coral reefs, seagrass flats and oyster beds, though one genus lives in cold seas. About half lack the famous weapon. In the rest, one claw grows to more than half the body length and works like a gun: a hinged hammer section cocks back to a right angle, held open by adhesive pads, then slams into a socket in the other finger.
The water jet it drives creates a cavitation bubble racing out at 25 metres per second, with acoustic pressure up to 80 kilopascals just 4 centimetres away. When the bubble collapses it gives off a faint, broad flash of light; if that were heat, the source would need to top 5,000 kelvin, roughly the Sun's surface temperature of about 5,772 kelvin. The glow is too weak to see with the naked eye. The strongest snappers carry a hood of shell over their eyes, which experiments suggest shields them from their neighbours' shockwaves.
Hunting is an ambush. The shrimp lurks in its burrow with antennae extended, feels a fish pass, creeps out and fires, then drags the stunned prey home. The same claw digs, bores rock, signals and fends off predators. Lose it, and the animal does something thought to be unique in nature: the small claw grows into a new snapper while the lost one regrows small.
Social lives are just as odd. Some species share burrows with gobies: the shrimp digs and keeps house, and the sharper-eyed fish flicks its tail to warn of danger while the shrimp keeps an antenna on it. In the genus Synalpheus, colonies of over 300 live inside sponges, all offspring of a single queen, with workers and soldiers like social insects.
Source: Alpheidae
