Snapping shrimps wear helmets to protect themselves from the shock waves produced by their claws.

Snapping shrimps appear to be immune to the shock waves produced by their claws, which can kill or stun other animals, thanks to their headgear.

Snapping shrimps have special headgear that prevents them from injuring themselves when they use shock waves to stun their prey.

Snapping shrimps
The hood over the eyes of this snapping shrimp (Alpheus heterothallic) protects it from shock waves. Taxonomist Crabby (CC BY-NC-SA 2.0)

Shock waves are created in the water by shrimps snapping their claws so quickly that they create popping bubbles that make a "snap" sound. These supersonic blasts of high-amplitude pressure - a very different type of force than physical impacts - can damage the shrimps' prey's brain, eyes, and gills, incapacitating or even killing the animal.

Surprisingly, the snaps appear to have no effect on the shrimp themselves, even when another shrimp snaps right next to their heads, according to Alexandra Kingston of the University of Tulsa in Oklahoma. She and her colleagues suspected that the hard, transparent hoods covering the animals' brains and eyes, which do not exist in other crustaceans, played a protective role.

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

According to Kingston, the behavior of these hoodless shrimp in the laboratory aquarium was essentially normal as long as there was no snapping. However, when the researchers enticed a shrimp to snap, the hoodless crustaceans in the same aquarium jolted, spun around, or fell over.

When these shrimps attempted to return to their shelters, they frequently appeared unable to coordinate their limbs and tended to get lost. Still-hooded bigclaw shrimp exposed to snaps in the lab, on the other hand, behaved normally. The hoodless shrimps took nearly seven times longer than the hooded shrimps to find shelter after a snap.

Using pressure sensors, researchers discovered that the pressure inside the hood was roughly half of what it was just outside the hood during a snap. According to Kingston, this suggests that the "helmet" has a strong protective effect.

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

These hoods are the only known biological devices that protect the brains of animals from the effects of shock waves. According to Kingston, the unique design could inspire better protective headgear for humans who work with explosives and other sources of shock waves.

"It's really difficult to stop these pressure waves," Kingston says. "Even traditional Kevlar cannot stop these shock waves." They are able to move through that material. My group hopes to collaborate with material scientists and engineers, as well as the military in the future, to create something that is more effective than just secondary [physical] blast injuries."

Reference: Current Biology, DOI: 10.1016/j.cub.2022.06.042


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