The mantis shrimp is a vibrant, 10-cm-long resident of the ocean whose look belies its popularity as one of the vital fearsome predators on the planet.
These unassuming crustaceans use a hammer-shaped appendage known as the dactyl membership to strike their prey at a blistering 23 m/s (about 50-times sooner than the blink of a watch), smashing into the poor creature’s physique like a bullet from a gun fired level clean. The strike releases sufficient energy to ship small shockwaves by means of the encompassing water.
But the factor about weapons is that each bullet fired has a recoil. It’s Newton’s third legislation of movement. If a firearm isn’t securely braced towards the physique to soak up it, the sudden backward movement can result in extreme accidents.
Yet regardless of putting prey arduous sufficient to provide shockwaves, the mantis shrimp stays unhurt. How is that this doable?
Lasers reveal a shield
A workforce of researchers from the US and France discovered the reply in a specialised microstructure within the mantis shrimp’s membership. They discovered that this construction was able to phononic shielding — a distinctive capacity that permits it to blunt the circulate of acoustic waves and thus weaken the recoil the mantis shrimp has.
Their findings had been reported in February in Science.
The workforce fired laser pulses on the microstructure in a fast sequence that illuminated its response at lower than one-billionth of a second at a time. They adopted this up with numerical simulations.
“People have looked at the material structure under a microscope but haven’t explored the dynamic mechanical behaviour, especially how it responds to wave propagation,” Maroun Abi Ghanem, the examine’s coauthor and a researcher on the Centre National de la Recherche Scientifique, France, mentioned.
“We looked into this behaviour by sending waves through the structure and analysed how they interacted with the material.”
Triggering implosions
The dactyl membership of a mantis shrimp shops its energy in spring-like elastic buildings held collectively by latch-like tendons. When the latch is launched, the membership is launched. As it strikes to ship its punch, it displaces the encompassing water and types small low-pressure zones. Inside these zones, the water’s density drops a lot that it turns into vapour, forsaking a bubble.
When these bubbles collapse as a result of strain of the encompassing water, they launch a appreciable quantity of warmth and shockwaves of very excessive frequencies, as much as a whole lot of megahertz.
Thus, every dactyl-club punch delivers two blows: one from its personal punch and the opposite from the collapsing bubbles, and collectively they’re able to breaking the robust shells of clams, mussels, and different crustaceans.
The dactyl membership has a hierarchical design — a fine-tuned mix of mineral and natural supplies organized in three layers. The outermost influence floor is fabricated from a skinny however arduous inorganic materials known as hydroxyapatite, which distributes the recoil and prevents it from accumulating at one level. Beneath it, the influence layer and the periodic area comprise biopolymer fibres organized in a sample that may stand up to repeated high-intensity influence with out incurring vital injury.
Previous research have explored the membership’s materials construction and influence resistance. The new examine went a step additional to examine whether or not the periodic structure of the supplies enhances its mechanical efficiency.
It does. The workforce discovered that the interior association of the microstructure serves as a phononic bandgap: a construction that stops energy waves of sure frequencies from passing by means of, or at the very least considerably attenuated, Horacio Espinosa, a examine coauthor and professor of mechanical and biomedical engineering at Northwestern University in Illinois, the US, mentioned.
‘An incredible example’
To mimic the ultrafast membership strike within the laboratory, the workforce used a pair of pulsed lasers that emit very quick flashes of sunshine: one to generate energy waves on the fabric floor and the opposite to detect them.
When the laser was directed onto a materials, it absorbed the sunshine and induced thermoelastic growth, i.e. heating and increasing the fabric. This generated a stress wave on the floor, like a miniature earthquake. The workforce tracked the wave’s motion by means of the shrimp’s membership to know energy switch within the materials.
The readings helped researchers draw dispersion diagrams — plots that exposed the bandgaps, or particular frequency ranges, the place waves couldn’t cross by means of or had been significantly weakened. The look of this sample within the information indicated to the workforce that the mantis shrimp used phononic shielding to guard itself from the recoil.
“What’s even more fascinating is that our findings suggest the club’s structure not only resists these intense forces but may also be fine-tuned to control how shock waves propagate through it,” Espinosa mentioned. “This dual role of structural robustness and wave manipulation is an incredible example of nature optimising materials at multiple levels.”
Here all alongside
For a very long time, scientists believed that supplies that would information the circulate of energy particularly methods might solely be created within the lab, not within the wild. Such supplies are known as metamaterials: they’ve specifically tailor-made geometries to realize these results. The new discovering concerning the mantis shrimp stands to vary this perception. Nature all the time had metamaterials.
The examine’s findings can also be utilized to develop artificial sound-filtering supplies to be used in protecting gear, corresponding to earmuffs for troopers. They might also encourage new approaches to lowering blast-related accidents within the military and sports activities, the researchers mentioned in a assertion.
“We are working on biomimetic structures inspired by the architecture of the mantis shrimp with a focus on wave trapping,” Abi Ghanem mentioned. “We are interested in understanding how the structures trap waves, explore what we can do with this trapped energy, and if it is possible to convert the trapped energy into another form.”
Sanjukta Mondal is a chemist-turned-science-writer with expertise in writing well-liked science articles and scripts for STEM YouTube channels.
Published – April 16, 2025 05:30 am IST
