Hydraenids are tiny beetles; the adults being less than 3mm long. The larvae are primarily terrestrial and are rarely recorded in streams. The adults are not designed for swimming (lacking streamlining or swimming hairs). The wing covers (elytra) cover almost the entire abdomen. The antenna has a club of 5 enlarged segments, but the maxillary palps (jointed mouthparts) are much more visible.
Hydraenids are common in many stony and gravelly streams, particularly in bush covered areas.
Hydraenids are thought to feed on plant matter (algae and/or terrestrial litter).
An abundance of Hydraenids is an indication of good water quality conditions, especially if there are also abundances of mayflies or stoneflies. They have tolerance values of 8 (hard bottom sites) and 6.7 (soft bottom sites).