Animal Crab strikes with the force of a small-caliber bullet
With tremendous force, mantis shrimps smash the shells of snails and mussels or kill fish. Even aquarium glass threatens to be shattered when these easily irritated creatures bang their clubs against it.
07.02.2025, 06:30
SDA
Why don't they break themselves? Clown mantis shrimps (Odontodactylus scyllarus) live in shallow, tropical waters and have club-like thickened legs. The colorful, up to 18 centimeters long animals are considered aggressive - some divers have reportedly been struck by them.
Blows with the force of a small-caliber bullet
The beautiful animals, which are popular with aquarium owners, are known for their tremendous striking power: Their clubs can strike at around 80 kilometers per hour with the force of a small-caliber bullet. The impact force can be equivalent to a thousand times the crayfish's body weight.
The clubs, which are clamped under the forebody when at rest, store energy in elastic structures that are held in place by tendons similar to bars. When the latch is released, the stored energy is released explosively and the club flings forward from under the body. This creates a low-pressure zone in the water behind it, in which a bubble forms.
Why do the shock waves not harm the crab itself?
The impact of the club on the target causes strong pressure waves, in addition to shock waves in the megahertz range caused by the collapse of the bubbles, explained co-author Horacio Espinosa from Northwestern University in Evanston. "This secondary shockwave effect, together with the initial impact force, makes the mantis shrimp's blow even more devastating." Nevertheless, no damage to tissue or nerves could be detected in the crustacean itself.
Research teams have been trying for some time to find out how the crustaceans can repeatedly strike with such force without destroying themselves. Earlier studies had already shown that the impact surface of the club is highly mineralized and contains a special sugar compound that makes the material less brittle.
The researchers led by Espinosa now used laser and ultrasound-based methods to investigate the microstructure of the carapace and the propagation of shock waves within it in more detail. The mantis shrimp's shell has two crucial areas: The impact area contains mineralized fibres arranged in a herringbone pattern. Below this are chitin fiber bundles that are offset against each other like corkscrews - this structure is also known as the bouligand from other animals such as lobsters.
Sophisticated structure of the leg
The herringbone pattern reinforces the club against breakage, the researchers explain. The spiral arrangement in turn determines how shock waves move through the structure. The result is a kind of protective shield that filters out high-frequency waves. This prevents the harmful vibrations from spreading into the arm and the entire body of the cancer.
The researchers hope that the results could help with the development of sound-filtering materials for protective equipment in the future. New approaches to reducing injuries caused by explosions are also possible.
Mantis shrimps are not the only crustaceans that work with shock waves: Pistol shrimps stun or kill prey fish with an extremely loud bang. These animals, which are only a few centimetres in size, also live in tropical waters and use one of their claws to create air bubbles that implode with a bang.
