Diving beetle (Rhantus)

Taxonomic group

Dytiscidae: Rhantus

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).

[Rhantus] adult. Image: Stephen Moore Image — Rhantus adult. Image: Stephen Moore

[Rhantus] larva. Larval cerci about as long as the last abdominal segment. Image: Stephen Moore Image — Rhantus larva. Larval cerci about as long as the last abdominal segment. Image: Stephen Moore

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

Hard bottom: 5
Soft bottom: 1.0

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

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).