If you want to find an ocean animal that kills with speed, don’t look to sharks, swordfishes, or barracuda. Instead, try to find a mantis shrimp. These pugilistic relatives of crabs and lobsters attack other animals by rapidly unfurling a pair of arms held under their heads. One group of them—the smashers—have arms that end in heavily reinforced clubs, which can lash out with a top speed of 23 metres per second (50 miles per hour), and hit like a rifle bullet. These powerful hammers can shatter aquarium glass and crab shells alike.
Most research on mantis shrimps focuses on smashers, but these pugilists are in the minority. The majority are “spearers”, whose arms end in a row of fiendish spikes, rather than hard clubs. While the smashers actively search for prey to beat into submission, the spearers are ambush-hunters. They hide in burrows and wait to impale passing victims. They’re Loki to the smashers’ Thor.
Given their differing lifestyles, you might expect the spearers to be faster than the smashers. They rely on quick strikes to kill their prey, and they target fast victims like fish and shrimp rather than the tank-like, slow-moving crabs favoured by smashers. But surprisingly, Maya DeVries from the University of California, Berkeley, found that the fastest spearer strikes at just a quarter of the speed of the fastest smasher.
For engineers looking to create the next generation of armour, the ocean is the place to look. Animals from snails to crabs protect themselves with hard shells whose microscopic structures imbue them with exceptional durability, surpassing even those of most man-made materials. They are extreme defences.
The mantis shrimp smashes them apart with its fists.
That’s the animal that David Kisailus from the University of California, Riverside is studying. “People have been studying molluscs for decades because they’re thought to be very impact-resistant,” he says. “The mantis shrimp eats these guys for dinner.”
Even the topmost layer of the ocean, just millimetres below the air above, is full of life. This zone, where two worlds meet, is home to small creatures like animal larvae, algae, bacteria, and other plankton. Among the most abundant residents of this zone are copepods – tiny relatives of crabs and shrimp. And some of them have the ability to leave this world altogether, and take to the air.
When threatened by fish, some copepods can jump straight out of the water and shoot over many times their own body lengths. From the fish’s point of view, its prey suddenly disappears. Flying fish use the same tactic to escape from predators. Now, we know that one of the most common groups of ocean animals shares their strategy.
I’ve got a new piece in Nature about a newly discovered species of “yeti crab” that farms bacteria on its arms, then eats them. It lives in the deep ocean, near seeps that belch out methane. The bacteria living on its bristly arms (hence the name “yeti crab”) feed off the seeping gases, and the crab encourage the bacteria to grow by rhythmically waving their arms.
Go to Nature to read the full piece. Meanwhile, I loved this quote from lead author Andrew Thurber, which gets across how much there is left to discover about the oceans: “It was a big surprise. There’s a tonne of them, they’re not small, and they’re six hours off a major port in Costa Rica.”
(Photos by Andrew Thurber)
Each of our eyes sees a slightly different view of the world, and our brain combines these signals into a single three-dimensional image. But this only works in one direction, because our eyes face straight ahead and their respective fields of vision only overlap in a narrow zone. But there was once a creature that had binocular vision in a massive arc around its body, not just in front but to the sides as well. It’s called Henningsmoenicaris scutula and it lived around half a billion years ago.
H.scutula lived in the Cambrian period, the part of Earth’s history when most of today’s major animal groups exploded into existence. It was a crustacean, one of the earliest members of the group that includes crabs, prawns and lobsters. It was just a millimetre long and almost totally encased within a bowl-shaped shield. From beneath the shield, weird spike-tipped legs propelled it along, while two stalked eyes, each just half a millimetre across, peered out at the Cambrian oceans.
These eyes are compound ones, made up of several units or ‘ommatidia’. They’ve also withstood the test of time. Their organic tissues have since been converted into the mineral apatite, and the resulting fossils perfectly retain the shape and angle of each ommatidium. The eyes are so well-preserved that Brigitte Schoenemann from the University of Bonn could use them to reconstruct how H.scotula saw the world to a “quite impressive degree”.
Releasing a steady stream of urine to attract a mate and then fighting off anyone who still dares to approach you doesn’t seem like a great idea for getting sex. But this bizarre strategy is all part of the mating ritual of the signal crayfish. A female’s urine, strange as it sounds, is a powerful aphrodisiac to a male.
Fiona Berry and Thomas Breithaupt studied these courtship chemicals by organising blind speed-dates between male and female crayfish, whose eyes had been covered with tape. They also injected a fluorescent dye into the animals’ bodies, which accumulated in their bladders. Every time they urinated, a plume of green dispersed through the water.
If the duo blocked the female’s nephropores (her urine-producing glands), the males never showed her any interest. If they met, they did so aggressively. But when the duo injected female urine into the water, things took a more lustful turn, and the males quickly seized the females in an amorous grip. Female urine is clearly a turn-on for males.
But the female doesn’t want just any male – she’s after the best, and she makes her suitors prove their mettle by besting her in a test of strength. As he draws near, she responds aggressively, even though it was her who attracted him in the first place. No quarter is given in these fights. The female only stops resisting if the male can flip her over so that he can deposit his sperm on her underside.
The most incredible eyes in the animal world can be found under the sea, on the head of the mantis shrimps. Each eye can move independently and can focus on object with three different areas, giving the mantis shrimp “trinocular vision”. While we see in three colours, they see in twelve, and they can tune individual light-sensitive cells depending on local light levels. They can even see a special type of light – ‘circularly polarised light’ – that no other animal can.
But Nicholas Roberts from the University of Bristol has found a new twist to the mantis shrimp’s eye. It contains a technology that’s very similar to that found in CD and DVD players, but it completely outclasses our man-made efforts. If this biological design can be synthesised, it could form the basis of tomorrow’s multimedia players and hard drives.
Previous studies have found that mantis shrimps can detect polarised light – light that vibrates in a single plane as it travels. Think of attaching a piece of string to a wall and shaking it up and down, and you’ll get the idea. Last year, scientists discovered that they can also see circularly polarised light, which travels in the shape of a helix. To date, they are still the only animal that can see these spiralling beams of light.
Its secret lies at a microscopic level. Each eye is packed with light-sensitive cells called rhabdoms that are arranged in groups of eight. Seven sit in a cylinder and each has a tiny slit that polarised light can pass through if it’s vibrating in the right plane. The eighth cell sits on top and its slit is angled at 45 degrees to the seven below it. It’s this cell that converts circularly polarised light into its linear version.
In technical terms, the eighth cell is a “quarter-wave plate”, because it rotates the plane in which light vibrates. Similar devices are also found in camera filters, CD players and DVD players but these man-made versions are far inferior to the mantis shrimp’s biological tech.
Synthetic wave plates only work well for one colour of light. If you change the wavelength slightly, they become ineffective, so designing a wave plate that works for many colours is exceptionally difficult. But the mantis shrimp has already done it. Its eyes work across the entire visible spectrum, from ultraviolet to infrared, achieving a level of performance that our technology can’t compete with.
What’s more, the same eighth cell not only manipulates circularly polarised light, but it can sense ultraviolet light too. It’s a detector and a converter – a two-for-one deal that nothing man-made shares.
Why the mantis shrimp needs such a sophisticated eye is unclear. It could help them to see their prey more clearly in water, which is rife with circularly polarised reflections. It needs good eyesight to be able to hit its prey accurately. Like a crustacean Thor, mantis shrimps shatter their victims with devastating hammer blows inflicted by the fastest arms on the planet. Their forearms, which end in clubs or spears, can travel through water at 10,000 times the acceleration of gravity and hit with the force of a rifle bullet.
Another option is that their super-eyes allow them to send and receive secret messages. A mantis shrimp’s shell reflects circularly polarised light, and males and females produce these reflections from different body parts. Their ability to see this type of light could give them a hidden channel of communication that only they can see, for use in courtship or combat.
Whatever the reason for it, Roberts thinks that the eye’s structure is “beautifully simple”. It’s all in the shapes of the cells, their size, and the amount of fat in their membranes. For all its outstanding performance, the eye’s abilities were probably easy to evolve, requiring only small tweaks to the basic blueprint of the light-detecting cells.
Now that we know about the microscopic structures behind the mantis shrimp’s amazing eye, Roberts is hopeful that engineers can mimic it using liquid crystals. “The cool thing is I think it’s actually something you could make and it would improve the workings of current technologies such as Blu-Ray, which uses multiple wavelengths of light, and of future data storage devices,” he said. It wouldn’t be the first time that crustaceans have inspired technology. A new type of X-ray telescope, for example, was based on the eye of the lobster.
Reference: Nature Photonics DOI: 10.1038/NPHOTON.2009.189
The amazing ways in which animals see the world
In April 1998, an aggressive creature named Tyson smashed through the quarter-inch-thick glass wall of his cell. He was soon subdued by nervous attendants and moved to a more secure facility in Great Yarmouth. Unlike his heavyweight namesake, Tyson was only four inches long. But scientists have recently found that Tyson, like all his kin, can throw one of the fastest and most powerful punches in nature. He was a mantis shrimp.
Mantis shrimps are aggressive relatives of crabs and lobsters and prey upon other animals by crippling them with devastating jabs. Their secret weapons are a pair of hinged arms folded away under their head, which they can unfurl at incredible speeds.
The ‘spearer’ species have arms ending in a fiendish barbed spike that they use to impale soft-bodied prey like fish. But the larger ‘smasher’ species have arms ending in heavy clubs, and use them to deliver blows with the same force as a rifle bullet.
Eagles may be famous for their vision, but the most incredible eyes of any animal belong to the mantis shrimp. Neither mantises nor shrimps, these small, pugilistic invertebrates are already renowned for their amazingly complex vision. Now, a group of scientists have found that they use a visual system that’s never been seen before in another animal, and it allows them to exchange secret messages.
Mantis shrimps are no stranger to world records. They are famous for their powerful forearms, which can throw the fastest punch on the planet. The arm can accelerate through water at up to 10,000 times the force of gravity, creating a pressure wave that boils the water in front of it, and eventually hits its prey with the force of a rifle bullet. Both crab shells and aquarium glass shatter easily.
As impressive as their arms are, the eyes of a mantis shrimp are even more incredible. They are mounted on mobile stalks and can move independently of each other. Mantis shrimps can see objects with three different parts of the same eye, giving them ‘trinocular vision’ so unlike humans who perceive depth best with two eyes, these animals can do it perfectly well with either one of theirs.
Their colour vision far exceeds our too. The middle section of each eye, the midband, consists of six parallel strips. The first four are loaded with eight different types of light-sensitive cells (photoreceptors), containing pigments that respond to different wavelengths of light. With these, the mantis shrimp’s visible spectrum extends into the infrared and the ultraviolet. They can even use filters to tune each individual photoreceptor according to local light conditions.
The fifth and six rows of the midband contain photoreceptors that are specialised for detecting polarised light. Normally, light behaves like a wave that vibrates in every possible direction as it moves along. In comparison, polarised light vibrates in just one direction – think of attaching a piece of string to a wall and shaking it up and down. While we are normally oblivious to it, it’s present in the glare that reflects off water and glass and we use polarising filters in sunglasses and cameras to screen it out.
Light can also travel in a the shape of a helix, moving as a spiralling beam that spins either clockwise (right-handed) or anti-clockwise (left-handed). This phenomenon is called ‘circular polarisation’. Tsyr-Huei Chiou from the University of Maryland found that the mantis shrimp’s eye contains the only known cells in the animal kingdom that can detect it. Our technology can do the same, but the mantis shrimps beat us to it by as much as 400 million years.