Japanese Diving Beetle
Cybister chinensis
An oarsman that dives carrying a bubble of air
The Japanese diving beetle is large and streamlined; its wing cases (elytra) and the shield behind its head (pronotum) are edged with a band of yellow. Though it never leaves the water for long, it breathes with air tubes (tracheae), surfacing to refill an air bubble beneath its elytra before diving back down.
Key figures
- Length
- About 35–40 mm, one of the larger diving beetles common in China
- Lifespan
- Adults can live for over a year, overwintering on the pond bottom or buried in mud
- Habitat
- Ponds, rice paddies, ditches and other still or slow-flowing waters
- Diet
- Carnivorous; preys on tadpoles, small fish and aquatic insects, with larvae consuming large amounts of prey
- Respiration
- Breathes with air tubes, surfacing to store air beneath its elytra and diving with the bubble in tow
- Swimming
- Flattened, paddle-like hindlegs fringed with long hairs stroke in unison to propel it forward
Life cycle
Egg → Larva (water tiger, aquatic) → Pupa (usually in soil near the shore) → Adult
Ecological role
Both adult and larval Japanese diving beetles are top predators in the aquatic food chain, consuming large numbers of mosquito larvae and small aquatic animals, and they are also fairly sensitive to changes in water quality.
Did you know
The larva is so fierce it is nicknamed the “water tiger”; when hunting, it plunges its sickle-shaped jaws into prey, injects digestive fluid, and sucks out the innards, leaving only an empty shell.
Range
Most of China, the Korean Peninsula and Japan
Status
Common
Anatomy
- Hindleg — Flattened like a paddle and fringed with swimming hairs; both legs stroke in unison to propel the body
- Elytra — Olive-black, edged with a band of yellow, with an air-storing space underneath
- Compound Eye — Fairly large, able to detect changes in light and shadow underwater while hunting
- Antenna — Thread-like and slender, used to sense air and scent when surfacing
- Air Store — The space between the elytra and the back, where it stores the air bubble it carries while diving
- Body — Streamlined and oval, reducing drag while swimming
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