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Diving beetle

Guide to New Zealand's freshwater invertebrates

Diving beetle ( Dytiscidae : Rhantus )

Larval cerci about as long as the last abdominal segment
Adult

Diagnostic features

Rhantus is one of the dytiscid “diving beetles” having larvae and adults that are active swimmers. The larvae lack any nose-like projection, and they have two tail-like cerci that are about as long as the last abdominal segment. The adults are oval and streamlined, 8 to 12mm long, with 11-segmented antennae, and the wing covers are mottled brown (lacking the strong stripes of Lancetes).

Typical habitats

Rhantus are most likely to be found in weedy ponds, and slow-flowing streams.

Feeding

The dytiscid beetles are predators, feeding on other pond invertebrates.

Indicator value

The presence of Rhantus is more likely to reflect pond-like habitat conditions rather than any particular water quality conditions. They have medium to low tolerance values of 5 (hard bottom sites) and 1.0 (soft bottom sites).