They are medium-small size insects; and not like the male, the female of C. vietnamica is very colourful; she has orange marking on the body with remarkable big marking on her thorax. The male is very simple in colour, with dull dark blue-violet marking on the body. In teneral form, the male are black with cream green marking. They wings are hyaline with somehow petiolate at base.
They live at clear swift streams in pristine forests of limestone mountain. Females of the species usually perch about 1.5 to 2 metres above water while males fly in the nearby forests. In rain season, the female is more common than the male.
Male, photographed by Cuong Do, Tam Dao National Park
Young male, photographed by Cuong Do, Tam Dao National Park
Female with orange marking thorax, photographed by Cuong Do, Tam Dao National Park