Elmidae

Elmidae, commonly known as riffle beetles, are a family of small to moderately large aquatic beetles in the order Coleoptera. They inhabit freshwater habitats, especially clean, fast‑flowing streams and rivers, though some species occur in springs, seepages, or still water. The group is distributed worldwide, with greatest diversity in tropical and subtropical regions. The family comprises numerous genera and hundreds of described species, including Elmis and Heterelmis.

Adults and larvae are aquatic throughout their life cycle. They are typically elongate and dorsally flattened, with a dark or brown coloration, and are commonly found clinging to submerged rocks, aquatic vegetation, or detritus in riffles and runs. They are adapted to underwater respiration and require well‑oxygenated water.

Ecology and biology: Elmidae feed largely on algae, biofilm, and decaying organic matter on submerged surfaces. Eggs are laid underwater on vegetation or debris; larvae and pupae develop entirely beneath the surface. In many species, adults possess wings that allow dispersal, although some lineages have reduced wings and are poor fliers.

Significance: Elmidae are sensitive to pollution and sedimentation, making them useful bioindicators in freshwater monitoring. They contribute to the stream ecosystem by participating in the breakdown of organic matter and forming part of the food web. Conservation of riffle beetles depends on maintaining clean, well-oxygenated water and protection of natural stream habitats.