[1] In Europe, R. suturalis coexists with the also-common species R. exsoletus, but that species has a vague black posterior margin to the pronotum instead of a central dark mark, and its abdominal sternites are yellow instead of black.

[3] In Australia, the only other Rhantus species is R. simulans, which is larger (12.8-13.5 mm) and only found in the country's southwest, unlike the more widespread R.

These hairs keep the rest of the pupa off the mud of the pupation cell (see the "Life cycle" section below), which may help it avoid fungal infection and keep the surrounding air fresh.

[6] Breeding occurs in spring and early summer, with eggs being deposited among submerged debris.

Towards the end of the larval stage, larvae become temporarily inactive, then leave the water to dig a cell in which pupation occurs.

The pupal stage may only last a few days, but adults remain inside the cell for a while longer to become pigmented and harden their exoskeletons.