Rhithrum

Rhithrum is a genus of mayflies (Ephemeroptera) belonging to the family Baetidae. These small to medium-sized mayflies are typically found in fast-flowing, well-oxygenated streams and rivers.

Characteristics:

• Nymphs (Larvae): Rhithrum nymphs are adapted for life in riffles and fast currents. They are streamlined and dorsoventrally flattened, allowing them to cling tightly to rocks and other submerged objects. Their bodies are typically brown or olive-green in color, providing camouflage against the streambed. They possess three caudal filaments (tails), though the median filament may be reduced in some species. The gills are typically located laterally on the abdomen.

• Adults: Adult Rhithrum mayflies are delicate insects with membranous wings. They have two or three long caudal filaments. Adults are short-lived, existing only long enough to reproduce. They are typically brown or grey in color.

Habitat and Distribution:

Rhithrum species are widely distributed in Europe and parts of Asia. They are indicators of good water quality, as they are sensitive to pollution. The presence of Rhithrum in a stream or river is generally a sign of a healthy aquatic ecosystem.

Ecology:

Rhithrum nymphs are primarily detritivores and grazers, feeding on algae and organic matter that they scrape from rocks and other surfaces. They are an important food source for fish and other aquatic predators. Adult mayflies do not feed and are primarily focused on reproduction.

Taxonomy:

The taxonomy of Rhithrum, like many mayfly genera, has been subject to revision over time. The genus includes several species, with ongoing research clarifying species boundaries and relationships.