June 2013, Mount Tam Dao, 1100m a.s.l, along a rocky, shaded stream.
For one hour or longer, I have been trying to get good shots of skittish males Caliphaea thailandica. As I was approaching carefully my 4th or 5th male, a large, black UFC (“unidentified flying creature”) appeared suddenly 15 meters away, close to the ground. I put my camera back in the bag, grabbed quickly my net and ran like crazy on slippery rocks. It was a large, black female dragonfly with striking black wings. She was flying slowly above shallow water, seeking a place to oviposit. An easy prey, even for a clumsy dragonfly hunter like me.
I captured the beast and was more than happy to discover inside my net a gorgeous female Chlorogomphus. A this time, the heavily-marked wings and the completely black abdomen remind me of the female of Ch. nakamurai. I snapped photos from every angle for further identification, and released her.
Vertex swollen (in the female Ch. nakamurai, the vertex shows an obvious pair of long protuberances). Antehumeral stripe almost disappeared and humeral stripe quite broad (broader than those of Ch. nakamurai).
One month later, Dô Manh Cuong sent me a paper of Karube about the genus Chlorogomphus in Indochina with description of 6 new species. Haruki Karube is THE specialist of Asian Chlorogomphids and Tam Dao is one of his preferred hunting ground in Vietnam. He described three new species from Tam Dao (Chlorogomphus takakuwai, Ch. sachiyoae, Ch. albomarginatus), which have never been recorded elsewhere* !
*update June 2014 : this is no longer the case. Ch. sachiyoae has been recorded this year at different other sites in northern Vietnam.
With this document, I confidently identified my guy as Ch. albomarginatus. This species has been described from Tam Dao in 1995, but has not been recorded since then - except maybe by Karube himself.
Abdomen almost wholly black, robust, especially in basal 3 segments.
Wings are broad, covered with deep black markings (Ch. nakamurai : dark-brown). Hind wings show a milky white band at the margin of this mark. Black mark of fore wings with a hyaline hole in the middle. No obvious blackish area at wings tips (unlike Ch. nakamurai).
Female Ch. albomarginatus resembles superficially to Ch. nakamurai, but can be easily separated by the head, the colour pattern of the wings, the pterothorax, ...
For a good comparison of the wings, have a look at this photo of a female Ch. nakamurai.
I think it really is a stunning dragonfly (and for once, the female is more beautiful than the male) and one I hope to bump into again. I will return at this stream next year and hopefully spot the male!
As I said above, Chlorogomphus albomarginatus is only known from Tam Dao. I spotted this female at a heavily shaded, rocky stream in steep terrain, in bamboo forest. Other interesting species noted there include Caliphaea thailandica, Coeliccia onoi, C. scutellum, C. acco, Indocnemis ambigua, I. orang, Rhipidolestes owadai, Devadatta ducatrix, Megalestes distans, Protosticta satoi, Agriomorpha fusca…
Many thanks to Dô Manh Cuong and Noppadon Makbun for providing documents!