kang (กั้ง)

Thai generic name for ‘mantis shrimp’, a semi-large marine crustacean, which despite its designation, is not a shrimp. It gets its name from its physical resemblance to both the praying mantis (fig.) and the shrimp. There are many species, all members of the order Stomatopoda and commonly divided into two groups, i.e. ‘spearers’ and ‘smashers’, the first with spiny appendages topped with barbed tips, used to stab and snag prey; the latter with a sharp-edged appendage used to cut prey, as well as a club to strike and smash their prey, and of which the blow has an acceleration that can be compared with the velocity of a bullet, purportedly able to break through aquarium glass with a single blow, and enabling it to open shells and clams on which it feeds. Scientists have measured the speed at 23 metres per second, the fastest strike in the animal kingdom. At this speed the blink of an eye would last 20 seconds. To accelerate to this speed the claw or spiny appendage experiences an incredible 8000 G and hits its prey with a force equivalent to a hundred times the equivalent of the shrimp's body mass. However, it is not the blow of the raptorial appendage in itself that cracks open the shell of a mollusk, but the speed of the blow causes the water to cavitate, generating a cavitation bubble that collapses super violently and fast, taking less than 5 milliseconds, creating a shockwave of energy so strong that it cracks open the shell. The bubbles collapse with so much power that they sometimes release a flash of light in a process called sonoluminescence. Cavitation happens when fast objects travel through fluids, creating an area of high pressure in the front and leaving behind it an area of low pressure, akin to the slip stream formed by a truck moving on a highway that will suck you forward behind it. As the static pressure of water is reduced, it will eventually change phase and vapourize, turning into a gas, thus forming cavitation bubbles. Mantis shrimps appear to be highly intelligent, able to learn and remember well. They exhibit complex social behaviour, such as the use of rituals in fighting, fluorescent patterns for signaling, etc. They are long-lived and some species are monogamous. Depending on the species, females either lay their eggs in a burrow or carry they around under their tail until they hatch. Mantis shrimps are common seafood and in Japanese cuisine they are eaten raw as sashimi and as a sushi topping. Hence, they are farmed or caught on a commercial scale. Species found in the Gulf of Thailand and the Andaman Sea, include Harpiosquilla harpax (Robber Harpiosquillid Mantis Shrimp or Oriental Krill), Harpiosquilla raphidea (Giant Mantis Shrimp), Miyakea nepa (Small-eyed Mantis Shrimp) and Oratosquilla nepa (Green Mantis Shrimp). Also called kang takkataen. 回