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Life in Freshwater

Riffle Beetle (Elmis aenea)

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Elmid Beetle hanging onElmid Beetle hanging on to stone in full river flow. Note large claws

These are small black beetles around 2 mm in length. They live under water and have long legs and strong hooked claws. They cannot swim. The larva is broad but flattened. Riffle Beetles are found in fast flowing water and along lake shores. They live permanently underwater and are surprisingly abundant in Europe wherever there is fast running rivers and streams.

ECOLOGY: These are true aquatic insects not requiring to come to the surface to air breathe. This holds true for both adults and larvae. The adult holds a small bubble of air under the wing cases which act as gills - the gases diffusing in and out of the water, called a plastron. Being so small the surface area to volume ratio is such that they can depend upon it. By contrast the Great Diving Beetle has to surface periodically. They are well adapted to survive in fast flowing water by virtue of the hooked claws on its legs. In this suspended form it moves along the bottom of stones and rocks. Here it feeds on algae and plant material. Note in the photo above the green algae on the stone












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