Today I visited Huu Lien Nature Reserve. It is still good, but for how much longer? The forest trail is now more and more a trail in the open sun, with more and more trees turned into charcoal by the locals. It is a sad affair. But anyway, in one of those open spots a noticed a gomphid perched on a leaf. It relocated, giving me a bit of a fright, but settled close by and I could catch it. In hand it reminded me of Fukienogomphus, a genus I had not yet seen. At home I checked the literature and Sebastien's blog. He has seen representatives of the genus twice in Tam Dao. The first thing I noticed was that Sebastien's specimens were much darker, with almost no yellow on the metepisternum. And the lateral processes on the superior appendages were also larger, the tips of the appendages darker. He had identified his specimens as F. promineus, which is rather larger than the other two known representatives, F. prometheus and F. choifongae. Cuong also recorded F. promineus from Mau Son in May 2010. He identified his specimens on their structural characteristics and size. And he notes that they are different from the Chinese specimens in the almost completely black metepisternum. They were in fact precisely the same as those observed by Sebastien.
My specimen was 61 mm in total length, with abdomen 46 mm (incl appendages) and hindwing 37. A little too large for F. choifongae. The inferior appendages are widely divaricate, way over 90 degrees, which sets it apart from F. choifongae, but my specimen, and in fact also the very dark specimens of Sebastien from Tam Dao, has black metakatepisternum. That should differentiate F. choifongae from the other two (Wilson 2006). Apparently that characteristic is variable (as is the antehumeral spot, missing both in my and in Sebastien's specimens). Based on the shape of the appendages, the posterior hamule and its measurements, I identified my specimen as F. prometheus. This is a common and wide-ranging species is China, and occurs in neighboring Guangdong and Hainan. It should not come as a surprise that it also occurs in Lang Son Province. It is thus the second species in the genus.
|Fukienogomphus prometheus, male, with extensively yellow on metepisternum, but black metakatepisternum.|
|Distinctive appendages in lateral view. Note the square ventral process.|
|And in dorsal view. Note widely divaricate inferior appendages and small lateral processes of the superiors|
|Black metakatepisternum and secondary appendages|