Not Exactly Rocket Science

i-b7aa155d6315a843b1369eee66a9e6a4-Revisitedbanner.jpg

Blogging on Peer-Reviewed ResearchIn 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.

i-a3845d67086764ddb685bf573167860a-Mantisshrim.jpgMantis 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.

Fastest claw in the west

When Sheila Patek, a researcher at UC Berkeley, tried to study these heavy-hitters on video, she hit a snag. “None of our high speed video systems were fast enough to capture the movement accurately” she explained. “Luckily, a BBC crew offered to rent us a super high speed camera as part of their series ‘Animal Camera’.” 

With this cutting-edge equipment, Patek managed to capture footage of a smasher’s strike, slowed down over 800 times. What she found was staggering. With each punch, the club’s edge travels at about 50 mph, over twice as fast as scientists had previously estimated.

“The strike is one of the fastest limb movements in the animal kingdom”, says Patek. “It’s especially impressive considering the substantial drag imposed by water.”

Water is much denser than air and even the quickest martial artist would have considerable difficulty punching in it. And yet the mantis shrimp’s finishes its strike in under three thousandths of a second, out-punching even its land-living namesake.

If the animal simply flicked its arm out, like a human, it would never achieve such blistering speeds. Instead, mantis shrimps use an ingeniously simple energy storage system. Once the arm is cocked, a ratchet locks it firmly in place. The large muscles in the upper arm then contract and build up energy. When the latch is released, all this energy is released at once and the lower arm is launched forwards.

But Patek found that even this system couldn’t account for the mantis shrimp’s speed. Instead, the key to the punch is a small, structure in the arm that looks like a saddle or a Pringle chip.

When the arm is cocked, this structure is compressed and acts like a spring, storing up even more energy. When the latch is released, the spring expands and provides extra push for the club, helping to accelerate it at up to 10,000 times the force of gravity.

Killer bubbles

This smasher’s arm is truly state-of-the-art natural technology. “Saddle-shaped springs are well-known to engineers and architects”, explains Patek, ” but is unusual in biological systems. Interestingly, a recent paper showed that a similarly shaped spring closes the Venus’s fly trap.”

Patek’s cameras revealed an even bigger surprise – each of the smasher’s strikes produced small flashes of light upon impact. They are emitted because the club moves so quickly that it lowers the pressure of the water in front of it, causing it to boil.

This releases small bubbles which collapse when the water pressure normalises, unleashing tremendous amounts of energy. This process, called cavitation, is so destructive that it can pit the stainless steel of boat propellers. Combined with the force of the strike itself, no animal in the seas stands a chance.

Large smashers can even make meals of crabs, buckling their thick armour as easily as they do aquarium glass. And they are often seen beating up much larger fish and octopuses, which are unfortunate enough to wander past their burrows.

Not just a good right hook

Some scientists think that the mantis shrimps’ belligerent nature evolved because the rock crevices they inhabit are fiercely contested. This competition has also made these animals smarter than the average shrimp. They are the only invertebrates that can recognise other individuals of their species and can remember if the outcome of a fight against a rival for up to a month. And since writing this piece, I’ve blogged about the amazing eyes of mantis shrimps, which have a way of seeing that’s unique in the animal world. One can only guess if these animals have other record-breaking adaptations that are yet to be discovered.

To find out more about mantis shrimps, check out the excellent Lurker’s Guide to Stomatopods.

This article won a runner-up prize in the 2005 Daily Telegraph Young Science Writer competition.

Reference: Patek, Korff & Caldwell. 2004. Nature 428: 819-820.

Update: At the time of writing, the mantis shrimp’s punch was a strong candidate for the fastest movement in the natural world. It has since been trumped by the bite of the well-named trapjaw ant, whose mandibles close with an almost unbelievable maximum speed of 140 mph. This discovery was made by none other than Sheila Patek. The mantis shrimp’s punch is still the world’s fastest limb movement, but the trapjaw ant’s jaws leave it dragging in its wake.

Comments

  1. #1 peter
    July 19, 2008

    the link to the shrimp footage appears broken…

  2. #2 Blind Squirrel FCD
    July 19, 2008

    How can cavitation occur in front of the shrimps’ limb? Isn’t the low pressure zone behind the limb?

  3. #3 natural cynic
    July 19, 2008

    a researcher at USC Berkeley,

    The University for Spoiled Children is in Los Angeles. Berkeley is the first campus of the University of California. Apologies are expected.

  4. #4 Matt
    July 20, 2008

    Yeah… I’m with Blind Squirrel. As far as I can see, the cavitation should be behind it. Can someone explain if this is a mistake, or how it can occur in front?

  5. #5 Ian Findlay
    July 20, 2008

    I seem to remember a whole series of articles on this published in the 60′s.

  6. #6 Ed Yong
    July 20, 2008

    Folks, I’ve changed the unfortunate USC Berkeley thing and the link to the videos. You may well be right about the cavitation thing but I’m on holiday on a rickety connection so I’ll check when I get back.

  7. #7 Thorfinn
    July 21, 2008

    I have the impression that the cavitation occurs post-contact on the withdrawal leg of the strike.

  8. #8 Mike Spear
    July 21, 2008

    For anyone interested here’s the actual video that Sheila Patek took at UC Berkley that started this whole fiasco:

    http://ist-socrates.berkeley.edu/%7Epatek/shrimpMechanics/5000fps.mov

  9. #9 Mike Spear
    July 21, 2008

    ….should have read the other comments first.

  10. #10 Matt
    July 21, 2008

    That may be Thorfinn, it makes sense to me.

  11. #11 Blind Squirrel FCD
    July 21, 2008

    The idea of cavitation on withdrawal of the leg doesn’t make sense to me. Does the shrimp have another set of fantastic muscles to withdraw the leg at light speed? Working in opposition to the deductor muscles? To what purpose?

  12. #12 Matt
    July 21, 2008

    It would only make sense if the shrimp could withdraw its leg quickly as well, which I’m assuming it could if the cavitation is indeed behind it like it says. I suppose it does have some muscle to retract it quickly, though not as quickly as it sends it out. I can’t think of a reason for this either.

  13. #13 Priam
    August 6, 2009

    Old thread, I guess, but hey.

    It looks like the cavitation comes at the point of impact, as seen in the Berkeley videos. Not a fluid dynamics specialist here, but my take is that when the arm strikes the shell, the sudden slam caves the shell rapidly inwards, causing water to rush to fill the impact zone, lowering the pressure and causing the water to go gaseous for a couple microseconds. There’s your cavitation.

    It doesn’t happen on the arm’s back-end, though, because, for one, the arm starts its movement more gradually, and two, the rounded shape means only a small amount is susceptible to strong pressure gradients at a time, whereas on impact the full impact zone is implicated in the pressure event.

  14. #14 Ken Kzak
    August 7, 2009

    Water is considered non-compressible. This is true when compared to air and even some other liquids, but if you push hard enough, it does compress, but it doesn’t have to like it.

    When you compress anything it creates heat. If you compress water enough it will exceed the boiling point, thus gas bubbles form. Since it’s producing light, this is near explosive levels in the confined micro zone between the Mantis shrimps claw and the surface under assault.
    This would constitute leading surface cavitation as opposed to trailing surface [negative pressure] cavitation.

    I once read where scientists [at least some jolly folks in lab coats] found they could produce light with intersecting sound waves in a small vessel of water. One sound source just pushes the water back and forth, two sources trap a tiny bit of water between them and compress it.
    Probably Discover Magazine about 15 years ago.