Just when you thought that pincers are just for picking items up, grabbing or crushing, think again!
The snapping shrimps or pistol shrimps (Alpheidae) are famed for their asymmetrical pincers. It has an enlarged pincer that can grow as long as half its body length and is capable of producing a loud snapping sound. What is so fearful of its huge pincer is not in its ability to crush, but its ability to act like a “pistol”. When the snapper claw extends into position and follows up with an extremely rapid closure, a high-velocity water jet is emitted from the claw with a speed exceeding cavitation conditions. This high-velocity water jet hits its prey animals with extreme pressure and temperature, and effectively stuns or kills them. Amazing! It is also this very action that produces its characteristic loud snapping sound, which is loud enough to affect naval sonar systems in submarines.
Such behavior by the snapping shrimp does not confine to attacking only, but also employed for defence and communication. The loud snapping sound wards off predators and potential territorial rivals of its kind. Interestingly, there is no concrete research to show that snapping shrimps have hearing organs. Instead, they have dense sensory hairs on their claw to pick up the vibrations from an opposing snapping shrimp. Two opposing snapping shrimps would “shoot’ at each other while maintaining a safety distance because their “duel” is not to annihilate or injure the other party, but to show who is the stronger of the two. The bigger the pincer, the larger the jet of water fired, the more powerful the "fire arm" and the stronger its owner. Sometimes, it is also through such battles that the snapping shrimp gets to befriend a female.
In that case, why not more? Well… since snapping shrimps dwell on seabed, they need to have traits that allow it to maneuver in such a terrain. For example, in addition to the pincer, the next limb (second thoracic limb) after the pincer is much longer, thinner and flexible, which allows the snapping shrimp to probe and reach for food that are concealed below the substrate. The remaining limbs also allow the snapping shrimp to move and burrow around just like normal shrimps.
Then the next question to ask would be… What happens if the shrimp loses that weapon of his? The fascinating thing about nature is that the other smaller claw would grow and replace the huge claw while the damaged one just recovers as a normal pincer. So perhaps the only thing the shrimp would need to do subsequently is to conduct more target practices with the other arm. BANG!!!
Reference:
“Pistol crabs use cavitation as a Navy shock: High Noon on the sea bed!” by Tobias Micke. Articles Extra, 22 Oct 2001.
“Snapping Shrimp Stun Prey with Flashy Bang,” by John Roach. National Geographic News, 3 Oct 2001.
D. Lohse , B. Schmitz & M. Versluis, 2001. Snapping shrimp make flashing bubbles. Nature, 413(6855):477-478.
A. T. Read, J. A. McTeague & C. K. Govind, 1991. Morphology and Behavior of an Unusually Flexible Thoracic Limb in the Snapping Shrimp, Alpheus heterochelis. The Biological Bulletin, 181(1): 158-168.
D. Schmitz & J. Herberholz, 1998. Snapping behaviour in intraspecific agonistic encounters in the snapping shrimp (Alpheus heterochaelis). Journal of Biosciences, 23(5): 623-632.
M. Versluis, B. Schmitz, A. von der Heydt & D. Lohse, 2000. How Snapping Shrimp Snap: Through Cavitating Bubbles. Science, 289(5487): 2114 – 2117.