Mantis shrimp clubs filter sound to protect themselves

Have you ever heard of the amazing mantis shrimp?

These incredible creatures can hit their prey with the same force as a .22 caliber bullet!  But here's something even more interesting - they don't hurt themselves when they strike, even though the force is extremely strong. 

Scientists at Northwestern University have found out why these small but powerful creatures don't get hurt from their own punches.Their special fighting arms, called dactyl clubs, have layers of patterns that work like a sound filter.These patterns are really clever - they block certain types of vibrations that could harm the shrimp, acting like a protective shield against the shock of their own hits.

The research will be published in Science journal on Friday (Feb. 7).

This discovery could help us create new protective materials for safety equipment. It might also help us find better ways to protect soldiers and athletes from injuries caused by strong impacts.

"Everyone knows mantis shrimp for their powerful hits - they're so strong they can break shells and even crack aquarium glass," explained Horacio D. Espinosa, who helped lead the study. "But what's really interesting is how they can keep hitting things without hurting themselves. While other researchers looked at how tough their clubs are, we found something new. These clubs have special structures that filter out harmful shock waves.   This helps the shrimp keep hitting things without getting hurt." 

Espinosa, who studies materials inspired by nature, is a professor at Northwestern's McCormick School of Engineering and leads the Institute for Cellular Engineering Technologies. He worked on this study with M. Abi Ghanem from the Institute of Light and Matter in France.

These fascinating creatures live in warm, shallow waters and have one hammer-like club on each side of their body. These clubs work like springs, storing energy that's held back by special tendons that work like locks. When these locks are released, all the stored energy bursts out, making the club move forward with incredible force.

With just one powerful hit, mantis shrimp can catch their prey or protect their home from unwanted visitors. When they punch, their club moves so fast through the water that it creates a special bubble in the area behind it where the water pressure is very low.

"When the mantis shrimp hits something, it creates waves of pressure that affect its target," Espinosa explained.

"It also makes bubbles that quickly burst and create shock waves at very high frequencies. When these bubbles burst, they release a lot of energy that goes through the shrimp's club. This second wave of shock, together with the first hit, makes the mantis shrimp's punch even more powerful."

Interestingly, this strong force doesn't hurt the shrimp's sensitive nerves and tissues, which are protected by its special armor. 

To understand this better, Espinosa and his team used two special methods to look closely at the mantis shrimp's armor. First, they used a technique called transient grating spectroscopy, which uses lasers to see how stress waves move through materials. Then, they used another method called picosecond laser ultrasonics to learn more about how the armor is built.

Their tests showed that the mantis shrimp's club has two different parts, each with its own job. The part that hits things is made of strong, mineralized fibers arranged in a pattern like fish bones, which helps it stay strong. Under this layer, there's another part with twisted bundles of fibers that look like corkscrews. These bundles are arranged in special layers, with each layer turned slightly compared to the ones next to it.

While the fish bone pattern helps stop the club from breaking, the corkscrew arrangement controls how stress waves move through it. This clever design works like a special shield that only lets certain waves through, stopping harmful vibrations from reaching the shrimp's arm and body. 

"The inner part of the club is really important because it blocks high-frequency waves that could hurt living tissues," Espinosa said. "This protects the shrimp from harmful stress waves caused by both the hit itself and the bursting bubbles."

In this research, the team looked at 2D models of how waves behave. Espinosa mentioned they need to do 3D models to fully understand the club's complex structure.

"We should focus future research on more detailed 3D models to really see how the club's structure deals with shock waves," Espinosa said. "Also, we need to do underwater experiments with modern equipment to see how these wave-blocking properties work when the club is in water."

The study, "Does the mantis shrimp pack a phononic shield?" received support from the Air Force Office of Scientific Research, the Office of Naval Research, and the National Science Foundation.

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Vietnamese Version of this post https://kenkai.vn/giai-tri/bi-mat-cua-vu-khi-tom-bo-ngua-loc-am-de-tu-bao-ve/ 

Source: https://news.northwestern.edu/stories/2025/02/mantis-shrimp-clubs-filter-sound-to-mitigate-damage