Last May, during a field trip in the foothills of Mount Ba Vi, I bumped into a cordulid dragonfly tucked away deep in the bushes. After some shots, I caught it for closer examination of caudal appendages, and identified a male Macromidia. I first thought it was M. rapida, a species I had seen along the same stream, but I noticed some obvious differences: cerci black (pale yellowish and black-tipped in rapida), face largely dark green, large yellow spot dorsally on S6.
Later, with the help of some documents (Fraser, Asahina), I confidently identified it as Macromidia genialis shanensis.
Macromidia species are crepuscular in nature and rest in dense vegetation near streams during day. They become active as rain threatens or dusk approaches, circling and zigzagging low over streams.
Head metallic dark green, except yellow labium and yellow anteclypeus.Synthorax marked on sides with 2 broad, green metallic stripes, enclosing a citron-yellow area; beneath (lower part of metepimeron) also citron-yellow.
Wings hyaline tinged with yellow at the base.
Abdomen black, with S7-9 inflated; S2 with a dorsal spot; S3-5 with a middorsal yellow longitudinal line; S6 with a large oval-shaped dorsal spot.
Anal appendages wholly black, of nearly the same shape as in M. rapida.
Tip of abdomen, dorsal
Male basal abdomen with secondary genitalia, lateral (M. rapida on the right for comparison). Note the shape of genital lobe: triangular in M. g. shanensis and rounded in rapida
Male head (right, M. rapida)
The genus Macromidia is purely oriental in distribution and contains a dozen of species, among them 2 has been recorded in Vietnam: M. genialis and M. rapida.
A number of subspecies of M. genialis have been described. Macromidia g. genialis is known from Peninsular Malaysia, M. g. erratica from Java, Sumatra and Sarawak, M. g. shanensis from Myanmar, Thailand, Laos, Vietnam (+China?).
The first record of M. g. shanensis in Vietnam is recent (in 2011, by Karube). Its inconspicuous nature may at least in part account for the paucity of records.
I found this male at a partially shaded, 3 meters wide rocky stream with well vegetated banks, but running through an open, heavily logged forest at the foothills of Mount Ba Vi. This suggests that this species do not require high quality habitats and therefore should be more common.