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 are most likely to be found in weedy ponds, and slow-flowing streams.
The dytiscid beetles are predators, feeding on other pond invertebrates.
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).