Snapping shrimps have helmets to ward off shock waves from their claws

Snapping shrimps seem immune to the shock waves their claws produce to kill or stun other animals – and it is all thanks to their head gear

By Christa Lesté-Lasserre

This snapping shrimp (Alpheus heterochaelis) has a hood over its eyes that protects against shock waves

Crabby Taxonomist (CC BY-NC-SA 2.0)

Snapping shrimps have special headgear that stops them hurting themselves when they stun their prey with shock waves.

The shrimps create shock waves in the water by snapping their claws so fast that they create popping bubbles that make a “snap” sound. These supersonic blasts of high-amplitude pressure – a very different kind of force from physical impacts – can damage the brain, eyes and gills of the shrimps’ prey, incapacitating or even killing the animal.

Curiously, though, the snaps don’t seem to affect the shrimps themselves, even when another shrimp snaps just next to their heads, says Alexandra Kingston at the University of Tulsa in Oklahoma. Suspecting that the hard, transparent hoods covering the animals’ brains and eyes – which don’t exist in other crustaceans – played a protective role, she and her colleagues investigated.

The team surgically removed these orbital hoods from 60 bigclaw snapping shrimp (Alpheus heterochaelis) captured off the coast of South Carolina.

The behaviour of these hoodless shrimp was essentially normal in the laboratory aquarium, as long as there was no snapping, says Kingston. But when the team enticed a shrimp to snap, the hoodless crustaceans in the same aquarium immediately jolted, spun around or fell over.

When these shrimps tried to move back to their shelters, they often seemed unable to coordinate their limbs and tended to lose their way. By contrast, still-hooded bigclaw shrimps exposed to snaps in the lab behaved normally. On average, after a snap, it took the hoodless shrimps nearly seven times longer to find their shelters than the hooded ones.

Investigations with pressure sensors revealed that the pressure inside the hood was about half what it was just outside the hood during a snap. This suggesting the “helmet” has a strong protective effect, says Kingston.

The key to this protection seemed to be in the hood’s holes just below the eyes. The water normally trapped inside the hood would gush out of the holes during shock waves, potentially redirecting the energy from the blast away from the brain and dampening its harmful effects.

These hoods are the only known biological equipment that specifically protects animals’ brains from the effects of shock waves. The unique design could inspire better protective headgear for humans who work with explosives and other sources of shock waves, says Kingston.

“It’s really hard to stop these pressure waves,” says Kingston. “Even things like traditional Kevlar armour don’t stop these shock waves. They can travel through that material. My group is definitely hoping to work with material scientists and engineers, and perhaps the military in the future, to try to engineer something that will be more effective than just protection against secondary [physical] blast injuries.”

Journal reference: Current Biology, DOI: 10.1016/j.cub.2022.06.042

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