Gomphidia kruegeri kruegeri Martin, 1904

G. kruegeri is a large-sized, build robust gomphid, marked with bright citron-yellow.

This is a wary insect, not easy to photograph, especially when only armed with a 100mm macro lens. But I finally found an individual which allow me to approach at very close range less than one meter away, for a full-frame image.

G. kruegeri can easily be confused by beginners with other large gomphids of the genus Gomphidia, Sinictinogomphus and Ictinogomphus.

Difficult to approach, G. kruegeri can be confidently identified in the field by using binoculars - that I always carry around my neck. Very useful tool, not only for birders ! Best option for dragonfly watchers are lightweight and close-focusing binoculars.

The key feature is the antehumeral stripe :  the oblique dorsal stripes joined to an upper humeral spot create a characteristic “boomerang” shape.

A male perched on a prominent twig facing the water, head inclined downwards

and abdomen held well up.

Dorsal and lateral views of caudal abdomen :
 

Superior appendages nearly twice the length of segment 10, flattened laterally, forcipate; inferior very short.

Abdomen dilated at base, then narrow and cylindrical as far as S6, terminal segments again dilated but without leaf-like expansions as in genus Ictinogomphus. S10 with 2 lateral spots.

Right after photographing this tame male, I caught a glimpse of a female for the one and only time. She entered the territory of the male. Immediately, he flew up and grabbed her, creating a sound like paper crumpling as their wings collide in a blur of movement - dragonfly sex is often a rough and tumble affair! Then, they retired to a nearby bush to consummate their relationship.
I got a shot but they quickly separated, visibly disturbed by my presence. 

I managed to get a single - crappy - shot of the female before she flew up.

G. kruegeri is known from northern Vietnam, central Thailand, north Laos, southwest and southern China. This is a widespread species found in forested and open aspect lowland and montane streams and river habitats.

G. k. kruegeri is separated from G. k. fukienensis Chao, 1955, by the form of the second yellow lateral stripe on the metepisternum of the synthorax, which is reduced to two small yellow spots, and a black postclypeus. G. k. fukienensis has a more extensive second yellow lateral stripe and its postclypeus has two large yellow spots (cf. ZHAO, 1990: 425-428).

In my area around Hanoi, this species is common along rock-bottomed streams with moderate to swift flow.