The mantis shrimp are not your ordinary shellfish, these colourful crustaceans rival sharks as the most deadly predators in the ocean. They have several incredible abilities that not only amaze scientists but are inspiring next generation technologies.
Is it a bird, is it a plane, no it’s… a shrimp? Now I know what you’re thinking shrimp can’t really fly and you are of course 100% right. But mantis shrimp do have several other incredible abilities that put them on the pantheon of the superheroes of the natural world. They have possibly pound for pound the most powerful punch in the animal kingdom with the equivalent force of a bullet and can strike so fast that they can even create sparks underwater. What’s more they have one of the most amazing visual systems on the planet capable of seeing polarized light and colours we couldn’t even imagine. These abilities make them one of the most feared and prolific predators in the marine world. But not only are these animals incredibly well adapted they are also inspiring the next wave of human technologies.
The first thing to clarify is that despite the name these amazing animals are not actually shrimp at all, they belong to the group stomatopods, and have more in common with lobsters than actual shrimp. The second thing to clarify is that we’re not talking about just one species but a group of around 500 different variations which share the same name. But collectively they all possess the same amazing adaptations that make them stand out as one of the most dangerous marine predators in the world. Most grow to around 10cm in length although some can get closer to 40cm and they come in a variety of colours from a basic brown to vivid multi-colour. Most live in tropical regions, especially on coral reefs, and despite being dangerous predators most species will spend their lives hidden from sight under rocks or buried in crevices.
What all mantis shrimp do have in common is a set of ‘raptorial appendages’, specially adapted arms either club or spear shaped, with which they deliver extremely powerful blows with at close range. These arms look similar to the front legs of a praying mantis which is where the group get their name. The other similarity between all species are extremely efficient compound eyes that allow them to see forms and wavelengths of light we and other animals cannot. They also have a thick tank like armour on their back that keeps them protected from attacks from above and are believed to be some of the most intelligent of all the crustaceans. Together these abilities make the mantis shrimp a formidable opponent for any similarly sized marine species.
Packing a punch
What makes mantis shrimp such great predators is their ability to incapacitate or even kill their prey with one lightning quick strike. The appendages that deliver the blow can either be blunted clubs or sharp spears but are equally lethal. They are capable of delivering one of the strongest and quickest punches in the animal kingdom capable of dismembering a crab or spearing a fish in the blink of an eye. It is believed that the punch lands at a speed of 50mph and delivers a force equivalent to a .22 calibre bullet. This is incredible especially considering how small the animals are and that it happens underwater, which is much denser than air. So how are they able to achieve such rapid speeds and incredible power?
The secret is how fast they can fully extend their arms. They are hinged and normally folded away beneath their head, but they can fully extend in less than one hundredth of a second which is what generates so much power. The mechanism behind this extension is a saddle like divot at the base of the appendages that acts like a bow and arrow. Extremely strong muscles ratchet the saddle back building up tension before releasing the stored energy and transferring it to the arm causing it to shoot outward. Because of how quickly the arm moves through the water something else amazing also happens which amplifies the power. The seawater in front of the arm decreases in pressure so rapidly it boils, creating what is known as a cavitation bubble. The bubble instantly pops releasing a flash of light and energy which acts like a miniature explosion. It is the combination of the rapid extension and the force of the cavitation bubble which enables the punch to be so powerful.
What is perhaps more impressive than the damage mantis shrimp can generate with their attacks is the lack of damage they sustain from performing them. The structures involved have to be very strong and durable to create the force needed for the punch and also reduce the impact on their own bodies. The arms have to absorb a lot of force in a punch to prevent any damage, especially those with a club like appendage. They can do this because of a specialized structure within their outer layer, which until it was discovered in mantis shrimp had never been seen in nature before. It consists of chitin arranged in a spiral like shape coated in calcium carbonate and phosphate. The result is a compound that can absorb a tremendous amount of force before breaking.
On the other hand the saddle has to be able to withstand a lot of tension to generate the rapid extension of the arm that makes it so deadly. It is able to do this because it is made of two very contrasting materials that complement one another in a very unique way. The top layer is a bioceramic, similar to the ceramics we use on a daily basis, and the bottom layer is a biopolymer, which is much more flexible. As the arm winds back into the saddle the bio ceramic layer compresses whilst the biopolymer layer underneath stretches to accommodate it. This allows the top layer to withstand much higher tensions than it would normally be able to. Without this arrangement of materials their attacks would be just a fraction of their speed and power.
I spy with my compound eye
But the amazing structures behind the mantis shrimp’s deadly attack are not the only ones scientists have taken an interest in. Their eyes are also incredibly well adapted and give them a sense of vision that is unrivalled by most marine creatures. Like other crustaceans, and most insects, mantis shrimp have compound eyes. This means they are made up of hundreds of different smaller units that collectively make an eye. In mantis shrimp these are rod like structures called ‘rhabdom’ that are themselves made up of stacked light receptors. What’s more whereas we have three different types of light receptors the mantis shrimp has twelve. The shape of the eye also unique with two hemispheres separated by a mid-band. Each hemisphere also slopes off at a 45 degree angle meaning a wider scope of vision.
There are several different benefits the mantis shrimp gain from having these adaptations. Firstly it allows them to see what is known as polarized light. Unpolarized light like sunlight has waves that travel in all directions but polarized light which can reflect of certain objects is unidirectional. Humans see polarized light as glare and cannot focus on its source however this is not a problem for mantis shrimp. Secondly the wider range of light receptors they possess also means they can register more wavelengths. This allows them to see more colours and even lets them see in the ultraviolet spectrum, which is very useful for locating prey against a dark blue background. Finally the position and angles of their eyes means they can perceive depth in space and focus on objects with only one eye. This gives them the ability to see both dark and light areas at the same time, which is very advantageous when you live in a dark crevice at shallow depths.
The mantis shrimp and their incredible adaptations allow them to dominate their niche in the marine ecosystem but they are now also starting to play a major role in our own world. Scientists have been fascinated with the species for decades and as they have unravelled the secrets to their success what they have found has inspired multiple real world applications. Most recently engineers from the University of Illinois have created a miniaturized camera capable of replicating the mantis shrimp’s incredible visual system. The one inch squared cube is capable of detecting polarized light and detecting a range of light intensities 10000 times greater than today’s commercial cameras. It is believed they could be used in hazard detection systems in cars, locating camouflaged targets with military drones and improving the safety of surgical procedures. What’s more this new device can be produced for as little as $10.
The unique materials that make up the arms and the saddle also have many real world applications. The impact absorbing structure in the outer layers of the shrimp’s appendages has inspired a synthetic version first created by the US air force to create better aircraft. However it has also been used to create body armour and even in NFL helmets to reduce the amount of concussions that players suffer in head on collisions. But with something as good as absorbing force as this the applications are virtually endless. On the other hand the bioceramic that makes up the top layer of the saddle has potential uses in robotics. Although it has not been replicated yet it is hoped that it will be able to replace some metal components, particularly in joints, as it is capable of withstanding similar tensions but is much lighter.
All of this means that mantis shrimp are not just marvels of the marine world but also helping to make ours a better place. If you want to see the mantis shrimp in action check out this short video by the Smithsonian channel.