<P> The adult beetles carry a bubble of air trapped beneath their elytra . This allows them to dive and swim under well - oxygenated water for indefinite periods if necessary . The mechanism is sophisticated and amounts to a physical gill . In practice though, their ecological adaptation is for the adults to scavenge and hunt on the water surface, so they seldom stay down for long . The larvae have paired plumose tracheal gills on each of the first eight abdominal segments . </P> <P> Generally Gyrinids lay their eggs under water, attached to water plants, typically in rows . Like the adults, the larvae are active predators, largely benthic inhabitants of the stream bed and aquatic plants . They have long thoracic legs with paired claws . Their mandibles are curved, pointed, and pierced with a sucking canal . In this they resemble the larvae of many other predatory water beetles, such as the Dytiscidae . Mature larvae pupate in a cocoon that also is attached to water plants . </P> <Table> <Tr> <Td> Hind leg of Gyrinus </Td> <Td> Antenna of Gyrinus </Td> </Tr> </Table> <Tr> <Td> Hind leg of Gyrinus </Td> <Td> Antenna of Gyrinus </Td> </Tr>

How many eyes does a whirligig beetle have