Cybister
Cybister ('kybistētēr' = diver, tumbler), is a genus of beetle in family Dytiscidae. They are found in much of the world, including all continents except Antarctica.[1][2] As of 2021 there are 96 species and 9 additional subspecies among four subgenera in the genus.[3]
Adult Cybister have broad hind legs with unequal tarsal claws (the inner claw being smaller and sometimes absent) and a fringe on the outer margin of the tarsus.[4] They range in length from 13 mm (C. parvus from Brazil) to 43 mm (C. bimaculatus from the Afrotropics).[5] Adult males of the North American species have several ridges on the coxae of the hind legs, forming a stridulatory device.[5]
Larvae have a frontal tooth on the head and lack cerci. North American species can grow up to 80 mm long.[4]
Like other diving beetles, Cybister are predatory. Larvae of C. japonicus prey on insects (mainly Odonata nymphs and the backswimmer Notonecta triguttata) in their first two instars, while third-instar larvae prey on vertebrates (tadpoles and fish).[7] Larvae of C. rugosus feed on both invertebrates and vertebrates in all instars.[8]
Cybister chinensis (sometimes misidentified as C. japonicus) is used in a game in Korea. The water beetle game (mul bang gae nori) is played in an oval, water-filled tank with vertical flanges along its inner edge and prizes on the tank rim. The game is played by dropping a C. chinensis through a funnel into the center of the tank, after which it swims towards the edge of the tank and stops in one of the slots formed by the metal flanges. If a prize is above this slot, the player wins it.[9]
The swimming behaviour of C. lateralimarginalis has inspired (biomimetics) the design of a legged underwater robot.[10]
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