Didelmis

Didelmis is a genus of riffle beetles in the family Elmidae. Members of this genus are aquatic beetles whose life cycle includes both larvae and adults that spend their entire lives in freshwater habitats, typically on submerged substrates such as rocks, wood, and vegetation in streams and rivers.

Taxonomy and identification within the Elmidae place Didelmis in the order Coleoptera. The genus comprises multiple described species, primarily from the American continents, and is the subject of ongoing taxonomic study as researchers document diversity across tropical and temperate freshwater systems.

Morphology and lifestyle are characteristic of many Elmidae. Didelmis beetles are generally small to medium-sized with a flattened, elongated body that helps them cling to substrates in flowing water. Their coloration ranges from dark brown to black, and their bodies are adapted to life in well-oxygenated streams, where both adults and larvae feed on biofilm, algae, and other periphytic materials.

Habitat and ecology of Didelmis species emphasize clean, fast-flowing water. They are often associated with riffles and fast currents, where their aquatic lifestyle and specialized appendages enable them to resist being swept away. Because they require well-oxygenated conditions, Didelmis species can serve as indicators of freshwater quality and ecosystem health.

Distribution is largely in the Americas, with many described species from Central and South American freshwater systems. Some species are found in North America and Caribbean regions as well. Ongoing taxonomic work continues to refine the understanding of their range, diversity, and ecological roles.