California Department of Fish and Wildlife
Aquatic Biological Assement

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Elmidae Level 1 Level 2






Key Characters (adult)

Riffle beetles. Found primarily in streams, although sometimes found in lake margins, some species associated with submerged wood. Adults ovate to elongate; small size, 1-8 mm; coloration black or brown, sometimes with bright red or yellow spots; head may be retracted into pronotum; antennae either short with 8 segments, or filiform with 10-11 segments; 5 visible abdominal sternites; sides of 4th or 5th sternites may be modified to grasp the underside of the elytra.

Key Characters (larva)

Larvae found in same habitats as adults; body shape generally cylindrical or hemicylindrical; body size ranges from 3-16 mm; 5-segmented legs, single claws; abdomen 9-segmented; sternites with pleural sclerites or sutures; urogomphi absent; last abdominal segment at least slightly emarginate; retractile anal gills covered by an operculum with internal hooks.

Tolerance variable, fom 1-6
Distribution CA, OR, WA, NV, AZ, Baja