Nihonogomphus - more widespread

To my not small amazement I caught a male Nihonogomphus schorri in Bac Kan Province on June 21. This species was described from Huu Lien, where it co-occurs with Nihonogomphus thomassoni. In early spring it was also very much in evidence in Xuan Son National Park. To my knowledge, Bac Kan is the third province in which this species is verified. Clearly the species has a distribution in northern Vietnam much larger than just Huu Lien in Lang Son Province.

Male Nihonogomphus schorri from Bac Kan Province

Some proof, appendages in dorsal view

In lateral view

In ventral view

And the distinctive shape of the lobe

 The other Vietnamese Nihonogomphus species was also very much present in northern Bac Kan Province. I am still not sure whether this taxon is Nihonogomphus lieftincki or N. thomassoni. In communication with various scholars the question has been raised whether these two species are really distinct. But for now let's go with the fact that N. thomassoni is the taxon said to occur in Vietnam. There was something peculiar about the really large number of specimens I saw in northern Bac Kan Province. Although I had seen this species in at midday in Huu Lien and on other streams in Lang Son Province, I think I saw it only once in Bac Kan during the day. One stream where it was very common I visited during the day half a dozen times, not to see any. But in the last 30 minutes or so before darkness it would appear in good numbers, with at least one every 25 meters or so and often several in close proximity, flying rapidly just above the surface chasing each other, or sitting on low hanging branches and shrubs over the water. They would still be there when it was almost too dark to see them. This seems at variance with their behavior in Lang Son, although I have not spent a lot of time there at dusk. Nevertheless, very peculiar. I also caught a female. Please compare to the female of the Nihonogomphus entry from Xuan Son. The lateral pattern on S3 is different.

Nihonogomphus thomassoni, female, Bac Kan Province

A very green male perched in almost complete darkness, but photographed with flash

Another male Nihonogomphus thomassoni in hand