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Riffle beetles

Guide to New Zealand's freshwater invertebrates

Riffle beetles ( Elmidae : Elmidae )

Larva with retractile hooks and gills
Adult antenna lacks a terminal club

Diagnostic features

Elmids are small beetles with long, slender, mealworm-like larvae. The larvae have retractile hooks and gill tufts under the last (9th) abdominal segment. The adults are aquatic, but not designed for swimming (lacking streamlining or swimming hairs). The wing covers (elytra) cover almost the entire abdomen. The antenna has no club of enlarged segments.

Typical habitats

Elmids are very common in many stony and gravelly streams, and can burrow deep into streambeds.

Feeding

Elmids are thought to be collector-gatherers, feeding on a range of fine organic matter trapped in the streambed.

Indicator value

Elmids can be found in high abundance in gravelly streams with moderate to good water quality. They have tolerance values of 6 (hard bottom sites) and 7.2 (soft bottom sites).