Heliogomphus retroflexus - about time

On May 10 I was checking a stream in central Ha Tinh Province when I noticed a freshly emerged gomphid landing by the side of the stream. I quickly made a few shots and checking them in preview it dawned on me that this must be Heliogomphus retroflexus. This is a species with a wide range, across Mainland China, Taiwan, Hainan, and south to at least Lao PDR and northern Vietnam. In fact the type was collected in Tonkin. But I had not seen it and was keen to do so, after it recently had been recorded from the Tam Dao mountain range by Natalia von Ellenrieder and colleagues. To find it relatively far south possibly extended its range. The stream I found it at ran through heavily disturbed woodland and plantations.

To my big surprise I ran into it again in Xuan Son on May 30, and not just one or two, but at least 10-15 individuals, all taking refuge from the heavy sun along the karst cliffs in the forest along the main stream. Not only several males and females, but also several copula were chilling there. It is not a difficult to recognize species, with the characteristic appendages of the male and the ringed abdomen. Strange to find it in such numbers in a place extensively surveyed last year.

Male Heliogomphus retroflexus. Apologies for the bad angle. They all tended to sit higher  up.

This female was more obliging

Not to speak of this very kind copula. 

This is the male in hand. Note the bulging lamina.

The appendages in dorsal view

The female, similarly ringed and with a golden wash to the wing bases. Note also the curvy hind femora.

The original teneral male from Ha Tinh. The ringed abdomen is already apparent.