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 gatheringperiphyton 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.
Adults with hardened forewings (elytra) covering the hind wings.
Terminal segment of each antenna no longer than combined length of 2 preceding segments; antennae thread-like.Elytra concealing entire abdomen or exposing only part of 1 tergite. Each leg with 5 tarsal segments, last tarsal segment about as long as other segments combined and with big claws. Abdomen with 5 visible segments.
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