The Dive Shack Tides: Creature Feature : Mantis Shrimp

Marine crustaceans of the Stomatopoda order, mantis shrimp were named for their physical resemblance to the praying mantis. They appear in a variety of colors from browns to bright neons, and may grow up to 12 inches in length. [1] Most species live in the tropical and subtropical waters of the Indian and Pacific Oceans between eastern Africa and Hawaii, although some live in temperate waters.

Fairly common animals, they often go unnoticed because they spend most their time hiding in burrows in the seabed or holes in rock formations. Important predators in shallow waters, mantis shrimp are known for their powerful claws which they use to attack and kill prey by spearing, stunning or dismemberment. [2] Unlike most crustaceans, mantis shrimp will not just wait for prey to happen upon their lair, but will actually leave their homes to hunt, chase and kill prey. They can be diurnal (active during the day), nocturnal (active at night) or crepuscular (active during dawn or dusk), depending on the species.

The mantis shrimp is often divided into two groups depending upon the type of claw they possess:

Spearers are armed with spiny appendages topped with barbed tips, used to stab and snag prey. They use their barbed claws to slice and snag the meat of softer animals, like fish.
Smashers, on the other hand, possess a much more developed club and a more rudimentary spear (which is nevertheless quite sharp); the club is used to bludgeon and smash their meals apart. Smashers use their ability to attack snails, crabs, molluscs and rock oysters.

Regardless of which group they are placed in, these shrimp use their claws to strike by rapidly unfolding and swinging them at their prey. They are quite capable of inflicting serious damage on victims significantly greater in size than themselves. Because they strike so rapidly, they generate cavitation bubbles between the appendage and the striking surface. [3] The collapse of these cavitation bubbles produces measurable forces on their prey in addition to the initial impact of the claw, which means that the prey is hit twice by a single strike; first by the claw and then by the collapsing cavitation bubbles that immediately follow. [4] Even if the initial strike misses the prey, the resulting shock wave can be enough to kill or stun the prey.

Strongest Punch in the World... [5]

Close-up of the trinocular vision of
Pseudosquilla ciliata
photographed by Shumpei Maruyama

Mantis shrimp have eyes mounted on mobile stalks which constantly move independently of each other and are considered to be the most complex eyes in the animal kingdom. [6][7] Designed with trinocular vision, they can see objects with three different parts of the same eye and have enhanced depth perception. They perceive both polarized light and hyperspectral color vision (more than red, green and blue bands of light). [8]

The eyes of mantis shrimp may enable them to recognize different types of coral, prey species (which are often transparent or semi-transparent), or predators, such as barracuda, which have shimmering scales. Alternatively, the manner in which mantis shrimp hunt (very rapid movements of the claws) may require very accurate ranging information, which would require accurate depth perception.

Mantis shrimp are long-lived. In a lifetime, they can have as many as 20 or 30 breeding episodes. Depending on the species, the eggs can be laid and kept in a burrow, or carried around under the female's tail until they hatch. Also depending on the species, male and female may come together only to mate, or they may bond in monogamous long-term relationships. [9] In the monogamous species, the mantis shrimp remain with the same partner for up to 20 years.

Mantis shrimp exhibit complex behaviour, such as ritualised fighting. Some species use fluorescent patterns on their bodies for signalling with their own and maybe even other species, expanding their range of behavioural signals. They can learn and remember well, and are able to recognise individual neighbors with whom they frequently interact. They can recognise them by visual signs and even by individual smell. Many have developed complex social behaviour to defend their space from rivals.

Hemisquilla ensigera californiensis - Californian Mantis Shrimp

How dangerous are the strikes of common mantis shrimps to humans?

"I handle stomatopods every day in our lab and when I'm in the field it is not uncommon to measure and sex 150 animals in an evening. Needless to say, I'm struck fairly often. Some species are far worse than others, but it usually hurts. Even a 2 cm Gonodactylus can draw blood and a 4 cm animal can drive the dactyl tips to the bone. Aside from a two inch slice in my hand made by a large lysiosquillid (by the uropod spine, not the dactyl), the most severe injury I have incurred was from a 7 cm Gonodactylus chiragra that drove its dactyl into the joint of my index finger and the tip broke off. It took some minor surgery to remove it. But that is nothing compared to what happen to a diver from South Africa who wrote me a few years ago describing his attempt to grab by hand an 18 cm Odontodactylus. The animal severely injured his finger which became infected by a chiton-digesting bacteria. The infection did not respond to the usual antibiotics. In the end, they amputated the finger. Be careful out there!

- Dr. Roy Caldwell

Web Site Author: A. Sunjian Note: There are newspaper reports of large Hemisquilla cutting off people's fingers with one strike, although how much credence can be given to stories like these is open to doubt."

References