Anax parthenope julius Brauer, 1865

The pond at Cat Ba Island where I took most of the photos below

In September 2013 I visited Cat Ba Island (southeastern edge of Ha Long Bay) and checking a wonderful pond in the National Park I observed many males Anax cruising. I first thought it was A. guttatus but their obvious smaller size cast doubts in my mind. Once in the hand it was clear that it wasn't the common guttatus but an Anax I had never seen before.
Females, unfortunately, weren't to be seen at the time of my visit.

A male, posed upon released

A male in hand

Note in the image above the reddish-brown femora, the abdomen with fawn lateral bands, the black stripe on top of frons, the unmarked bright green thorax (olivaceus-brown thorax in the nominotypical subspecies). 

Compare with the male Anax guttatus in the photo below. In general appearance, especially when seen on the wing, A. parthenope is very similar to A. guttatus. Both have a very noticeable blue saddle at S2 and S3 which really stands out in flight. Once in hand, both show green eyes and an unmarked yellow-green thorax, but there are striking differences in color pattern of abdomen, legs and frons - not to mention the structure of anal appendages.   

Anax guttatus : sides of abdomen spotted, femora almost entirely black, frons entirely green

A. parthenope julius is also smaller than A. guttatus (abdomen : 50 cm vs 60 cm in my specimens), and its flight gave me the impression to be more erratic, less powerful than that of guttatus.

Anax partenope julius, male. This really is a truly magnificent creature.

Male, facial pattern. Note the multi-colored upper surface of frons

Anax guttatus, male, facial pattern. Frons entirely yellow-green.

Male parthenope julius, anal appendages, dorsal & ventral views. Epiproct very short, very broad, toothed apically, one-fourth the length of superiors, paler than superiors, the latter with a spine at the outer side of the apex. Note also the "U" shaped marking on dorsum of S10.

Anax guttatus, anal appendages. Cerci not much different from those of parthenope but epiproct of completely different shape and proportionally longer. Dorsum of S10 unmarked.

Anax partenope julius exuviae

A. parthenope is a wide-ranging species, known from southern Europe and North Africa to the Arabian Peninsula, Siberia, India, China and Japan. In the east of its Asian range (including Vietnam, China, Taiwan, Japan, Korea, Southern Far East Russia, South Siberia) the subspecies A. parthenope julius occurs, which might prove to be a distinct species.

In Russia, the Transbaikalian records concern A. parthenope julius, the Central and West Siberian records concern the nominotypical subspecies (Kosterin, 2007).

In Vietnam, I am aware of some records in Vinh Phuc (Tam Dao) and Lang Son Provinces. Considering its distribution (Northeast Asia), it is very likely that A. parthenope julius only occurs in the northern part of the country.

To my knowledge, 4 Anax species were recognized in Vietnam*, viz. the South Asiatic A. guttatus (common),  A. parthenope julius (apparently much less common than guttatus but likely to be under recorded due to its resemblance with the latter), A. nigrofasciatus (upland species, blue saddle at S2-S3 also but body blacker than guttatus and parthenope) and A. immaculifrons (color pattern completely different than the 3 others - orange abdomen and wide stripes to the thorax). 

*update April 2016: now 5 species with the discovery of A. indicus in Hanoi (record not yet published)

Considering its range (from Japan to Indonesia), A. panybeus is also very likely to be present in Vietnam. This open-pond species is very much like A. guttatus. This is how to distinguish it based on Dr. Orr’s guidebook "Dragonflies of Peninsular Malaysia and Singapore":

1) distinct ‘T’ on the dorsal part of the frons;
2) third abdominal segment more constricted and distinctly longer;
3) male appendages differ slightly.

In conclusion, all the `A. guttatus` should be captured for in-hand examination. I know that it is a hard and time-consuming job but chasing Anax species is a perfect way to improve netting skills. It is also great fun!