The peacock mantis shrimp is both beauty and the beast. It's a highly effective aquatic killing machine wrapped in an eye-candy package. With 250 million years of evolutionary history behind it, the peacock mantis shrimp has figured out how to find and kill prey with stunning skill -- and it looks good doing it.
The peacock mantis shrimp has a uniquely strong and fast offensive weapon in its hammer arms. A system of latches keeps the arm muscles flexed until ready to fire. When the latch releases, the arm launches forward at speeds up to 45 mph -- the fastest moving strike system of any animal on Earth. Pent-up muscle tension coupled with saddle-like springs on the upper arm deliver crushing death strikes. A blow from Odontodactylus scyllarus can deliver as much force as a 22-caliber bullet. Dr. Sheila Patek, a biologist who has extensively studied the mantis shrimp, believes this animal could set a record for producing the greatest amount of force in proportion to the size of its body. With such force the shrimp can easily crack open snail shells, its primary prey.
The mantis shrimp's super-fast, powerful strike is possible because of two systems within the arm -- the latch and the saddle. The saddle is a structure on the shrimp's upper arm that's surrounded by membranous tissue and works like a spring. Most of the time the spring is contracted, but when the latch is released the saddle expands, amplifying the force behind the arm's launch. Patek has noted that the peacock mantis shrimp can use the brightly colored spots in the middle of its saddles as a way to communicate. The shrimp waves its arms, decorated with the spots, as a bluff to potential threats. The crustacean uses this bluff when it's about to molt -- a time when crustaceans are highly vulnerable.
Because the peacock mantis shrimp can move its arms so quickly, it creates cavitation bubbles with each strike. Cavitation occurs when water is accelerated to a much faster speed than the water around it. This produces bubbles that, when they collapse, cause small implosions of light, heat and sound. In less than 800 microseconds, Odontodactylus scyllarus delivers a four-fold attack -- one physical hit from each hammer arm followed by dual bubble blasts from the cavitation.
Maintaining the Weaponry
It's logical to assume the body part delivering such powerful blows will undergo some serious wear and tear. In the case of the peacock mantis shrimp, its hard exoskeleton covers the hammer arms, but after several strikes this shell is worn away. Odontodactylus scyllarus molts every three months, and when it does it builds a new hard shell, renewing its weapons.
The mantis shrimp has the most complex eyes in the animal kingdom. It's able to see the UV and infrared light spectrums. O. scyllarus has 16 kinds of photoreceptor cells, 12 of which are specialized for different colors. Its eyestalks can move independently of each other, expanding its field of view. The eye is also divided into three parts that perceive motion, forms, depth and color. Male mantis shrimp can see light in a way unlike any other animal -- they can see circular polarized light, so for these crustaceans, it's like they're able to put on a pair of 3D glasses to see with an extra layer of depth. Researchers haven't determined yet why male mantis shrimp have this ability, but because it's a sex-specific trait, the reason for it is most likely related to mating.
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