They may be colorful and small, but mantis shrimp are not to be trifled with. These carnivorous crustaceans pack a powerful punch that can smash mollusk shells at speeds of up to 50 miles per hour and even break glass. Yet the shrimp’s bodies remain intact despite the blowback from their hits.
Now, a team of scientists have uncovered the secret to their impressive physical resilience. Their fists are covered in layered patterns that can selectively filter out sound. Blocking out specific vibrations ultimately creates a pattern which acts like a shield against the shockwaves generated by their powerful punches. The findings are detailed in a study published February 7 in the journal Science.
Sending shockwaves
There are over 400 known species of mantis shrimp. These creatures with spectacular vision are found in shallow, tropical waters around the world, where they feed on various crabs and snails. Most species are about four to seven inches long, while some can reach up to 15 inches.
Mantis shrimp are armed with a one hammer-like dactyl club on each side of its body, which act like a pair of fists and can punch with the force of a .22 caliber bullet. The dactyl clubs store energy in elastic, spring-like structures held in place by latch-like tendons. When the tendons are released, the stored energy is let go with it, propelling the club forward.
With one blow, the mantis shrimp can defend their territory or kill its prey. When the punch rips through the water, it creates a low-pressure zone behind it and a series of bubbles.
“When the mantis shrimp strikes, the impact generates pressure waves onto its target,” study co-author and Northwestern University engineer Hoacio D. Espinosa said in a statement. “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.”
Surprisingly, this huge striking force does not damage the shrimp’s delicate nerves and tissues encased within the shrimp’s armor.
Shielding patterns
In the new study, the team used two advanced techniques to look at the mantis shrimp’s armor in fine detail. First, they used transient grating spectroscopy. This laser-based method analyzes how stress waves spread through materials. Next, they deployed picosecond laser ultrasonics. This method gave further insights into the armor’s microstructure.
Within the mantis shrimp’s club, they found that there are two distinct regions that are each engineered for a specific function–the impact region and the periodic region.
The impact region is responsible for delivering the crushing blows and consists of mineralized fibers arranged in a herringbone pattern. This pattern gives it resistance to any failures. The periodic region is just beneath this layer. It features twisted, fiber bunches similar to a corkscrew. The bundles form a Bouligand structure–a layered arrangement where each layer is progressively rotated relative to its neighbors. These structures are also seen in other crustaceans like lobsters.
The herringbone pattern reinforces the club against fractures. At the same time, the corkscrew arrangement controls how stress waves from the punch travel through the structure. This intricate design acts as a shield that selectively filters out high-frequency stress waves to prevent damaging vibrations from moving 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 said. “This effectively shields the shrimp from damaging stress waves caused by the direct impact and bubble collapse.”
[ Related: Bullet-fast mantis shrimp punches caught by super-speed cameras. ]
Learning from mantis shrimp
The team analyzed 2D simulations of wave behavior in this specific study. However, the authors believe that 3D simulations in additional studies are needed to fully comprehend the club’s complex structure.
“Future research should focus on more complex 3D simulations to fully capture how the club’s structure interacts with shockwaves,” Espinosa said. “Additionally, designing aquatic experiments with state-of-the-art instrumentation would allow us to investigate how phononic properties function in submerged conditions.”
These findings could be applied to developing synthetic, sound-filtering materials for protective gear in the figure. It could also be used to design new approaches for reducing blast-related injuries in the military and in sports.
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