Imma Perfetto
Cosmos science journalist
Mantis shrimps dole out a punch powerful enough to break mollusc shells and even crack aquarium glass, while somehow avoiding injuring itself in the process.
These carnivorous marine crustaceans of the order Stomatopoda come in 2 flavours – “spearers” and “smashers”. Spearers impale prey on their toothed claws, while smashers clobber theirs.
There are more than 500 species worldwide, found on coral reefs or on the seabed to a depth of 1,500m.
New research has discovered how smashers withstand the intense shockwaves created by their own striking fists, known as dactyl clubs.
“When the mantis shrimp strikes, the impact generates pressure waves onto its target,” says Horacio Espinosa of Northwestern University in the US, co-corresponding author of the study presenting the findings in the journal Science.
“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.
“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.”
Esponosa and collaborators found it uses “phononic” mechanisms, structures that selectively filter stress waves, instead.
“This enables the shrimp to preserve its striking ability over multiple impacts and prevent soft tissue damage,” says Espinosa.
They closely examined the armour of the peacock mantis shrimp (Odontodactylus scyllarus), a species found in the Indo-Pacific seabed that range from 3-18cm in size.
They found that the outer impact region of the dactyl club consists of mineralised fibres arranged in a herringbone pattern, which reinforces the club against fractures. Beneath this, the periodic region is made of twisted,corkscrew-like fibre bundles that that act as a “phonic shield”.
“The periodic region plays a crucial role in selectively filtering out high-frequency shear waves, which are particularly damaging to biological tissues” Espinosa says.
“This effectively shields the shrimp from damaging stress waves caused by the direct impact and bubble collapse.”
While the researchers analysed 2D simulations of wave behaviour, Espinosa says that 3D simulations are needed to fully understand the club’s complex structure and how it interacts with shockwaves.
“Additionally, designing aquatic experiments with state-of-the-art instrumentation would allow us to investigate how phononic properties function in submerged conditions,” he says.
