Researchers have established that mantis shrimp clubs filter sound to mitigate damage. The patterned armor of the shell selectively blocks high-frequency stress waves.
The fact that the mantis shrimp can withstand repeated high-impact forces without structural damage could inspire advanced protective materials for reducing blast-related injuries.
Mantis shrimps are carnivorous marine crustaceans of the order Stomatopoda. Known for their powerful punch, the mantis shrimp can smash a shell with the force of a .22 caliber bullet. What has puzzled scientists for a long time is how the shrimp itself remains intact despite the intense shockwaves created by its own strike?
Northwestern University researchers have discovered how mantis shrimp remain impervious to their own punches. Their dactyl clubs are covered in layered patterns, which selectively filter out sound. By blocking specific vibrations, the patterns act like a shield against self-generated shockwaves. Could this observation within nature inspire something for humans to utilise?
Researchers hope the findings can be applied to developing synthetic, sound-filtering materials for protective gear as well as inspire new approaches to reducing blast-related injuries in military and sports.
“The mantis shrimp is known for its incredibly powerful strike, which can break mollusk shells and even crack aquarium glass,” explains lead researcher Horacio D. Espinosa.
Espinosa adds: “However, to repeatedly execute these high-impact strikes, the mantis shrimp’s dactyl club must have a robust protection mechanism to prevent self-damage. Most prior work has focused on the club’s toughness and crack resistance, treating the structure as a toughened impact shield. We found it uses phononic mechanisms — structures that selectively filter stress waves. This enables the shrimp to preserve its striking ability over multiple impacts and prevent soft tissue damage.”
What happens when the shrimp strikes?
“When the mantis shrimp strikes, the impact generates pressure waves onto its target,” Espinosa clarifies. “It also creates bubbles, which rapidly collapse to produce shockwaves in the megahertz range. The collapse of these bubbles releases intense bursts of energy, which travel through the shrimp’s club. This secondary shockwave effect, along with the initial impact force, makes the mantis shrimp’s strike even more devastating.”
Understanding the phenomenom
To investigate the activity, Espinosa used two techniques to examine the mantis shrimp’s armor in fine detail. First, they applied transient grating spectroscopy, a laser-based method that analyzes how stress waves propagate through materials. Second, they employed picosecond laser ultrasonics, which provide further insights into the armor’s microstructure.
These experiments revealed two distinct regions — each engineered for a specific function — within the mantis shrimp’s club. The impact region, responsible for delivering crushing blows, consists of mineralized fibres arranged in a herringbone pattern, giving it resistance to failure. Beneath this layer, the periodic region features twisted,corkscrew-like fibre bundles. These bundles form a Bouligand structure, a layered arrangement, in which each layer is progressively rotated relative to its neighbors.
While the herringbone pattern reinforces the club against fractures, the corkscrew arrangement governs how stress waves travel through the structure. This intricate design acts as a phononic shield, selectively filtering high-frequency stress waves to prevent damaging vibrations from propagating back into the shrimp’s arm and body.
“The periodic region plays a crucial role in selectively filtering out high-frequency shear waves, which are particularly damaging to biological tissues” Espinosa observes. “This effectively shields the shrimp from damaging stress waves caused by the direct impact and bubble collapse.”
In this study, the researchers analyzed 2D simulations of wave behavior. Espinosa said 3D simulations are needed to fully understand the club’s complex structure.
Going forwards
“Future research should focus on more complex 3D simulations to fully capture how the club’s structure interacts with shockwaves,” Espinosa predicts. “Additionally, designing aquatic experiments with state-of-the-art instrumentation would allow us to investigate how phononic properties function in submerged conditions.
Research paper
The study “Does the mantis shrimp pack a phononic shield?” is published in the journal Science.
