Riffle beetles (Elmidae)

Taxonomic group

Family: Elmidae

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.

Riffle beetle (Elmidae). Adult antenna lacks a terminal club. Image: Stephen Moore Image — Riffle beetle (Elmidae). Adult antenna lacks a terminal club. Image: Stephen Moore

Riffle beetle (Elmidae) larva with retractile hooks and gills. Image: Stephen Moore Image — Riffle beetle (Elmidae) larva with retractile hooks and gills. Image: Stephen Moore

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

Hard bottom: 6
Soft bottom: 7.2

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

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).