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. As of 2021 there are 96 species and 9 additional subspecies among four subgenera in the genus.

Description

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. They range in length up to 43 mm (C. bimaculatus from the Afrotropics). Adult males of the North American species have several ridges on the coxae of the hind legs, forming a stridulatory device. Larvae have a frontal tooth on the head and lack cerci. North American species can grow up to 80 mm long.

Ecology

Cybister live in lentic (still fresh water) habitats that have vegetation. 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). Larvae of C. rugosus feed on both invertebrates and vertebrates in all instars.

Importance

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. The swimming behaviour of C. lateralimarginalis has inspired (biomimetics) the design of a legged underwater robot.

List of species

Subgenus Cybister Curtis, 1827

Subgenus Megadytoides Brinck, 1945

Subgenus Melanectes Brinck, 1945

Subgenus Neocybister K.B. Miller, Bergsten & Whiting, 2007

Fossil species

These seven extinct species are known only from fossils: