Moss beetles (Hydraenidae)

Taxonomic group

Family: Hydraenidae

Diagnostic features

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.

Moss beetle (Hydraenidae). Image: Stephen Moore Image — Moss beetle (Hydraenidae). Image: Stephen Moore

Moss beetle (Hydraenidae). Maxillary palps of adult extending well in front of head. Image: Stephen Moore Image — Moss beetle (Hydraenidae). Maxillary palps of adult extending well in front of head. Image: Stephen Moore

Typical habitats

Hydraenids are common in many stony and gravelly streams, particularly in bush covered areas.

Feeding

Hydraenids are thought to feed on plant matter (algae and/or terrestrial litter).

Indicator value

Hard bottom:8
Soft bottom: 6.7

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

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).