Saturday, 22 November 2014

A whole lotta Ceriagrion! A new visit to Cat Tien National Park

12 to 18 November we were guests in the Forest Floor Lodge in Cat Tien and spent all day in the field looking for dragonflies, now under very different conditions than in the wet season. Everyday was filled with sunshine and the forest was already very much drier, with most ponds having disappeared, the Dong Nai River showing expanse of rocks in the rapids, and streams in the forest reduced to trickles. During the wet season I had seen 3 species of Ceriagrion, now we were hoping for a few more. And indeed, we encountered 6, 4 of which I had not seen before. One of the first was a species with bright red abdomen and red face, first seen at the pond in the lodge garden and later also encountered elsewhere. Using Asahina's (1967) summary of Ceriagrion I made a startling discovery. It keys out as, and otherwise also fits very well, C. chaoi. But I had already seen that species, and it was very different in coloration, as far as I knew. So I went back to that species too and checked it once more. In side view the appendages are very much the same, but in dorsolateral view the shape of the superiors is in fact different. I had misidentified the species I had seen in Xuan Son, in the north of Vietnam. That was not C. chaoi at all, but C. bellona, a species known from Sumatra and Borneo, also recorded from Malaysia (see Asia Dragonfly and IUCN). I have also found photos of it taken in Thailand, so it seems C. bellona has a more extensive range than generally known and may occur all over south-east Asia. Be that as it may, what I now consider C. chaoi is identical to specimens identified as such and published through photographs on the web from Singapore. I also found several photos identified as "much redder than usual C. praetermissum" from Thailand. These have a red face and greenish thorax sides, something not present in C. praetermissum. It would appear these too are C. chaoi and are identical to those from Singapore. Clearly this species also ranges to southern Vietnam. It was observed at two locations, but clear water ponds in forested environment with a lot of water plants.

Male Ceriagrion chaoi, note red face, bright red abdomen, greenish flanks and brownish dorsum
Another male
Another male, showing the bicolored thorax and red face
Appendages of C. chaoi in lateral view. Very similar to C. bellona.
But see the triangular subapical process to the superiors in dorsolateral view, rather different
The second species I ran into was very small Ceriagrion praetermissum. The male of this species also has red abdomen and red face, but has otherwise pale brownish tones. This appears to be a dry season species, that now was very common around the larger lakes, like Crocodile Lake and Bird Lake. There were still many fresh individuals in the forest or hiding in the grass. It may well be abundant in a little while. The appendages of the male and female are quite distinctive. The female has a long ovipositor and the male has a characteristically forked inferior appendage. Apparently C. praetermissum was not yet known from Vietnam, but it is common in neighboring countries.

Male Ceriagrion praetermissum with brownish thorax, but orange-red abdomen and red eyes.
Another male
Female C. praetermissum, with long ovipositor and red eyes.
Very characteristic inferior appendages of C. praetermissum
The next new species I ran into was the long-bodied Ceriagrion olivaceum. This species is as big as C. praetermissum is minute. I only saw three fresh individuals, all males, but as this is also a dry season species, it may likely become more common a little later in the season. This species has rather pale eyes and the abdomen does not become reddish.

Long-bodied male Ceriagrion olivaceum with greenish eyes and only marginally orange-brown abdomen.
Another fresh male.
The appendages of the male
The last, and a very spectacular, new species was Ceriagrion cerinorubellum. This is a beautiful green and orange species, rather large, with characteristically long inferior appendages. Not that this plays a role in its identification, its size and coloration rule out other species at a glance. I saw only two in a drying out pond with extensive rush-fields.

Spectacular Ceriagrion cerinorubellum, striking and beautiful.
Another male, with a dark spot on the thorax.
The two other species I encountered were C. malaisei, of which I saw a single male at Crocodile Lake that I could not take a picture of, and C. aurantiacum, which too I saw at Crocodile Lake, but in somewhat larger numbers, and at the fishponds.

Green-eyed Ceriagrion aurantiacum
Another male in dorsal view
And the lateral view of the appendages, with the relatively long and straight inferiors

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