Great Diving Beetle

• fisiologíaIt stores a bubble of air under its wing cases, which lets it breathe underwater for long spells while it hunts small invertebrates.
• Its larva, known as the water tiger, has hollow jaws with which it injects digestive enzymes into its prey and then sucks out the liquefied tissue.
• It flies between ponds at night, and sometimes mistakes the gleam of a wet roof or a dark car for the surface of the water.
• It breathes from a tank. It rises to the surface back first, pokes the tip of its abdomen out and stores a bubble of air beneath its elytra, which serves it both as a reserve and as a physical gill: oxygen from the water diffuses into the bubble while it dives.
• It is a fearsome predator for its size: it attacks tadpoles, insect larvae and small fish, and can kill prey larger than itself.
• The larva is even more voracious and is known as the water tiger. It has hollow mandibles through which it injects digestive enzymes and then sucks up the liquefied prey.
• The male's front legs are fitted with suckers with which it grips the female's back during mating; she usually has grooved elytra, and it has been proposed that those grooves are a counter-adaptation to make this harder.
• It flies well, mostly at night, and colonises new ponds. It sometimes mistakes shiny surfaces such as car roofs or greenhouses for water and lands on them.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Ponds, pools and still, vegetated backwaters

Size at birth

The larva reaches up to 60 mm, nearly twice the length of the adult

Gestation / incubation

The eggs, inserted one by one into the stems of submerged plants, take 17 to 19 days to hatch; the larva goes through three instars and pupates in damp soil at the water's edge

Litter / clutch size

The eggs are laid one by one into incisions made with the ovipositor in the stems of aquatic plants; in the family Dytiscidae up to 1,000 eggs per female are reported

Sources consulted: Natural History Museum de Londres; Buglife; Bergsten y Miller (2007), PLOS ONE; First Nature; datos de la familia Dytiscidae; First Nature, ficha Dytiscus marginalis; guias de identificacion; EBSCO Research Starters, ficha Great diving beetle; Ficha de especie de Dytiscus marginalis

Best time: The young adults emerge from the pupa in mid-autumn but stay buried until spring; they fly at night and navigate by the moon's reflection on the water