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Shrimp spring into shattering action
Q: Can a mantis shrimp really punch a hole in its
aquarium glass? I mean, how can it? (Lanney, Sandia Park, New Mexico)
 A: The sun lights the shallow seafloor off the coast of Bali.
About 10 yards (10 m) down, an emerald-green body roams the bottom with blue
eyestalks extended and green antennae waving. The hungry peacock mantis shrimp
spots prey; she cocks her red, hammer-like forelimb; ready.
The peacock mantis shrimp peers forward with orange eyes
and probing antennae. Her red, hammer-like forearm is in its up, locked position
(see arrow).
Larger image. Courtesy of Roy Caldwell, copyright, used with permission.
A small, creamy, brown-spotted snail (confident within his
thick spiral shell) inches along the seafloor in his slow-one-footed way. The
predator closes fast, and hovers above the snail. The mantis shrimp (who isn’t a
shrimp) releases her spring-loaded hammer-like claw; it flashes forward — too
fast to see — in an underhand blow that smashes the snail’s shell with a loud
bang.
The speed of the strike (up to 50 mph, or 23 m/s) creates
cavitation bubbles between the shrimp’s hammer-like heel and the struck snail.
The bubbles collapse, and generate heat, light, and sound. The shell shatters
with a flash too-fast-to-see, and a bang. Watch the flash (called
shrimpoluminescence for another species) in the
video,
slowed by a factor of 900. (Courtesy of Sheila Patek, Wyatt Korff and Roy
Caldwell/UC Berkeley) Though the mantis shrimp’s tough heel is impregnated with
hard minerals, still she must shed the pitted, damaged surface every few months,
and grow new heel armor.
Yes! Certainly, a mantis shrimp (more elegantly known as a
stomatopod) can break aquarium glass.
"There are a half dozen species capable of breaking a standard
glass aquarium," says biologist
Roy Caldwell
a professor at the University of California at Berkeley. Including, of course,
the peacock mantis, which gets about 7 inches (17 cm) long.
Caldwell, S.N. Patek and W.L. Korff discovered how the mantis
shrimp generates such powerful blows. It isn’t muscle power alone. In fact, the
mantis shrimp (a crustacean, distantly related to lobsters, crabs and shrimp)
needs 470,000 watts of power per kilogram of muscle to do the job — orders of
magnitude higher than the fastest-moving muscles can deliver. The creature’s
weapon needs much energy delivered fast.
 So, how? She stores the energy, and then releases it in a
flash like a sprung jack-in-the-box. Clever. The animal latches the hammer limb
so it can’t move. She contracts her muscle as much as she can (compressing the
jack-in-the-box). This much stored energy could hurt her limb, but doesn’t
because of another clever device.
Mantis shrimp have evolved a special saddle-shaped spring
that, due to its shape, can distribute huge loads over its surface without
buckling or failing. See circled area in the figure and the next figure, which
shows the saddle and the modeled spring. When she frees her latched limb and
spring, she releases the stored energy fast, and the red, hammer-like claw
lashes out at blinding speeds, smashing her hapless prey.
The black circle indicates the location of the mantis
shrimp’s special saddle spring, limb lock, and limb hinge. The mantis shrimp’s
two eyes gaze out at the top of the picture. Her long, hammer-like claw swings
forward, breaking glass in Caldwell’s aquarium. Courtesy of Roy Caldwell,
copyright, used with permission.
 Back to breaking glass. When mantis shrimp dig on the seafloor
and run into an obstacle, they strike it to try to break it and remove the
obstacle, says Caldwell. So, typically, when an animal starts digging in an
aquarium corner, she encounters glass. This "usually leads to their whacking the
glass, chipping it, and just causing a leak." A few mantis shrimp though, over
the years, have shattered the aquariums. "This usually happens when they attack
their reflection or when they try to hit a teasing finger waving at them through
the glass."
The top drawing shows the actual saddle-like structure of
the mantis shrimp’s leg that acts like an extremely tough spring. The bottom
drawing shows the modeled spring. Courtesy of Roy Caldwell, copyright, used with
permission.
By the way, praying mantises and mantis shrimp, though evolved
along entirely different paths, share the same spring-like strike mechanism.
Further Reading:
How a praying mantis hunts, WonderQuest
S.N. Patek, W.L. Korff, R.L Caldwell. "Deadly strike mechanism
of a mantis shrimp." Nature, vol428, 22 April 2004.
University of California:
Secrets of the Stomatopod by Roy
Caldwell
Wikipedia:
Pistol shrimp and shrimpoluminescence
UC Berkeley News: Mantis shrimp may have swiftest kick in the
animal kingdom by Robert Sanders.
Edge-of-Reef.com:
Peacock mantis shrimp
Odontactylus scyllarus
(Answered Jan. 3, 2005)
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