The family Psephenidae comprises small to medium-sized beetles that are closely associated with clear watercourses. Whilst the adults live near water on riparian vegetation or stones, have reduced mouthparts (they usually do not feed) and are often overlooked due to their inconspicuous appearance and short lifespan, their larvae are truly unique within the insect kingdom. Thanks to their extremely flattened, almost circular bodies, which resemble tiny coins, they have earned the name ‘water pennies’ in English. This shape allows them to cling perfectly to the surface of stones in fast-flowing streams, where they withstand the force of the water thanks to a hydrodynamic suction effect. The larvae live mainly in very well-oxygenated flowing water, particularly on stones and wood in rapids and faster-flowing streams, where they feed primarily on algae and the fine organic coating on the stones. The larvae are sensitive to pollution and sedimentation in watercourses – their presence is considered an indicator of clean, well-oxygenated waters (they are among the most characteristic aquatic beetles of mountain and foothill streams). On a global scale, this is a family with high diversity in the tropics; however, in the conditions of Central Europe and the Czech Republic, it is a very rare and localised group, represented by a single species.

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Eubria palustris