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Moss beetles

Guide to New Zealand's freshwater invertebrates

Moss beetles ( Hydraenidae : Hydraenidae )

Maxillary palps of adult extending well in front of head

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.

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

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).