Can a snapping shrimp really make a bubble as hot as the Sun?

Some of the loudest animals in the ocean are about the size of your little finger. Snapping shrimp live in huge colonies in warm, shallow seas, and together they make a constant crackling noise, like bacon in a pan. For a long time people assumed the sound came from the claw slamming shut. It doesn’t. The real source is a bubble, and that bubble briefly gets astonishingly hot.

The short answer

When a snapping shrimp snaps its oversized claw, it shoots out a fast jet of water. The pressure in the jet drops so low that a cavitation bubble forms. When that bubble collapses, it makes the bang, and a team of physicists estimated that the gas inside heats up to around 5,000 kelvin. The Sun’s visible surface is roughly 6,000 kelvin.

The real story

In 2000, physicists at the University of Twente in the Netherlands, working with colleagues in Germany, filmed shrimp snapping with high-speed cameras and recorded the sound at the same time. Their paper in Science showed that the noise does not happen when the claw closes. It happens a moment later, when the bubble collapses. The claw is really a water pistol, which is why these animals are also called pistol shrimp.

The following year the same group, led by Detlef Lohse and Michel Versluis with Barbara Schmitz, reported in Nature that the collapsing bubble also gives off a tiny flash of light. They nicknamed it shrimpoluminescence. The flash is far too faint and brief for human eyes, and it had to be picked up with a very sensitive light detector. From the light, the researchers estimated the extreme temperature inside the bubble.

Before anyone imagines a shrimp setting the sea on fire: the bubble is minuscule and lasts a tiny fraction of a second, so the heat vanishes almost instantly. What matters to the shrimp is the shock wave. The blast is used to stun small prey, to fight rivals and even in finding mates. The Twente group notes that snaps can reach source levels of around 200 decibels, though underwater decibels are measured differently from those in air, so the number is not directly comparable to a rock concert.

Why people get it wrong

If you hear a crack from something with a claw, the natural guess is that the claw made it. It is the same logic as clapping your hands. Before high-speed cameras could freeze the moment, nobody could see that the sound came a split second after the claw closed.

The temperature claim also sounds like the sort of exaggeration that spreads online, so many people quietly assume it is made up. In this case, the headline is based on a peer-reviewed estimate. It is the scale that surprises: sun-like heat, yes, but in a tiny bubble, for far less time than a blink.

“A shrimp with a water pistol that briefly rivals the Sun. I can’t even work a stapler.”