A stunning Megalestes with the majority of thorax coloured bright metallic green, which is pruinosed with oily whitish deposits in mature males.
Male, without flash - more natural appearance I think.
Male, with flash - sharpness and contrast increase.
Abdomen of male dull reddish (blackish at intersegmental sutures) except S1-2 green metallic on dorsum and S8-10 dark brown.
Dorsal synthorax and mesepimeron metallic green (with orangey highlights when the light is right!) with humeral (mesopleural) suture black. Metepimeron and metepisternum pruinosed white, except a short horizontal dark green stripe (which does not reach the spiracle) on the latter.
Prothorax blackish with central lobes with metallic green reflections. Posterior lobe pale yellowish.
Anal appendages blackish brown ; superiors slightly longer than S10, forcipate with basally, on the inner side, a short quadrate process. Inferior appendages much shorter, with two pairs of curved spines in lateral view.
I encountered the female on 2 occasions. The photos below of an ovipositing female were taken in September along a forested stream (< 1 m wide), at the first slopes of Tam Dao so at a very low altitude (ca 200m).
She is very similar to male and also brightly coloured with metallic green but white pruinosity on sides of synthorax is replaced by yellow and the abdomen is duller.
Megalestes distans is known from China (Guangdong, Guangxi, Guizhou, Henan, Hubei, Hunan, Shaanxi, Shandong, Sichuan, Yunnan, Zhejiang) and several localities in northern Vietnam.
I mostly encountered the males in August (the wettest month here in northern Vietnam), at montane and submontane well shaded streams – but one time as low as 200m a.s.l. (ovipositing female).
The closest congener of Megalestes distans is M. haui Wilson & Reels, 2003 (described from Guangxi), which has similar overall colouration and similarly shaped superior appendages. The two species can not be confidently separate without study of penile organ.
At Ba Vi and Tam Dao, only M. distans has been recorded. In Vietnam, M. haui is known, at least, from Sa Pa (Lao Cai Province) (Dô Manh Cuong, pers. comm.).
Other Zygoptera species spotted there (in August): Anisopleura qingyuanensis, Cryptophaea vietnamensis, Noguchiphaea yoshikoae, Coeliccia acco, C. onoi, C. scutellum, Atrocalopteryx coomani, Protosticta satoi, Devadatta ducatrix, Agriomorpha fusca, Drepanosticta sp.
Earlier in the season (May, June), remarkable Anisoptera species were recorded there, such as Merogomphus tamdaoensis, Chlorogomphus auratus and Sinorogomphus nasutus satoi.