I spotted this stunning species in mid-August 2012 and September 2013, at Sa Pa (Lao Cai Prov., northern Vietnam), within the Hoang Lien National Park boundaries, a bit below Tram Tôn Pass (Đèo Trạm Tôn), at ca 1900m a.s.l.
In October 1995, Syoziro Asahina also vouchered a male in the same area ("Deo Tram Ton"). It was the second record of this species after its original description in 1930 (type locality is Sichuan) !
I used a part of his description publish in « Records of the Northern Vietnamese Odonata taken by the expedition members from the National Science Museum, Tokyo, 1996. Part III : Aeschnidae, Corduliidae, Libellulidae” for writing this post.
The males were flying slowly, hovering a lot
Male, in hand
Thorax shining metallic green with broad yellowish bands on the sides.
Abdomen entirely metallic black, except some yellow markings on S2 and S3 as follows : S2 with a lateral yellow spot and a yellow edge along the posterior margin; two proximal spots laterally on S3.
Male, tip of abdomen, dorsal and lateral views
Somatochlora dido has an extremely broad and fragmented distribution from northern Vietnam through southwestern and southern China (Guangdong, Guangxi and Sichuan) and Hainan. All confirmed records have been obtained from high altitude in remote locations. Only a few scattered locations are currently known, but the species is probably under-recorded.
Members of the genus, the largest in the Corduliidae, are predominantly Holarctic and they are found as far north as Odonata exist. When found in the subtropics these species has been usually found at high altitude in excess of 1000 m up to 2290 m (source : http://www.iucnredlist.org).
At Sa Pa, I found this species at an acidic wooded swamp in a small valley.