“Riffle Beetles”
Family Overview
Elmidae
Riffle Beetles
This is a large family, including 24 genera and close to 100 species. They are known as riffle beetles, due to their common occurrence in habitats with fast-flowing water and high oxygen levels. Both larvae and adults are slow-moving clingers that feed by scraping or collecting and gathering periphyton and detritus from surfaces of rocks and other substrates. The larvae get their oxygen directly from gills that can be retracted into the end of the abdomen. Adults have an effective plastron and usually do not need to surface for air. Elmid larvae are unusual in that they have up to 8 instars, whereas most beetle larvae molt only 3 times.
Characteristics
POLLUTION TOLERANCE
Mid-Atlantic: 2 - 6
Upper Midwest: 3 - 6
Midwest: 2.75 - 4
Southeast: 1.1 - 6.9
0 = least tolerant, 10 = most tolerant
FEEDING HABITS
Collector / Gatherer
Scraper / Grazer
Shredder / Herbivore
Scraper / Grazer
Shredder / Herbivore
MOVEMENT
Climber
Clinger
Clinger
Diagnostic Characters
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