Riolus subviolaceus (Mueller, 1817)
Family: Elmidae
Size: 2.1 mm (1.9 to 2.1 mm)
Distribution: Europe
Ecology: Lives in cold calcareous mountain streams
Location: England, Sharpenhoe
leg.det. P.Harwood, 30.IX.1928
Coll. Oxford University Museum of Natural History
Photo: U.Schmidt, 2015

Riolus subviolaceus  (Flickr)