Saturday, March 5, 2011

--. Aciagrion occidentale (Laidlaw, 1919)

Number: --
Family: Coenagrionidae
Genus: Aciagrion
Species: Aciagrion occidentale (possibly)
Common name(s): Asian Slim
Thai name(s): แมลงปอเข็มเรียวผู้ฟ้า
Habitat: Exposed ditches, drains, ponds and lakes (uplands & lowlands)
Province(s) sighted: Mukdahan NP (Mukdahan)
Sightings (by me): Uncommon
In flight (that I have seen): October

The fourth damselfly (potentially) from the Aciagrion genus I have seen, is Aciagrion occidentale. As mentioned in my previous post it is very difficult to distinguish between A. occidentale and A. borneense. 

The male
The male does have a very slight tinge of green dorsally on the thorax, but is very pale compared to that of A. borneense. The ocular stripe is also slimmer, as too is the abdomen. Otherwise, the two look alike. 

The female
The abdomen is slightly slimmer than that of A. borneense. The ocular stripe is also slimmer. I could be completely wrong, however!

I have seen this species at Mukdahan National Park. It is a small, slim species that you have to look for carefully.

Since I posted this page, Oleg Kosterin believes this still to be A. borneense. Though probably correct, I will leave this post up for the time being. Maybe someone can shed even more light on the species.

As I cannot confirm as of yet whether this is or is not A. occidentale (or a different species altogether) I cannot count it as a separate species ... hopefully one day.


  1. I am still convinced this is A. borneense as well. I never paid attention to the slimness of abdomen and occiputal stripe, but the differences are too slight if any, while the intensity of blue increases with a damselfly age. Maybe the 'thicker' and paler individuals are just younger ones. (Or even maybe there is a cryptic species which is not occidentale). A. occidentale is a mostly Indian species very rare in Thailand and reported from summer ( while borneense mostly from the dry season), it is noticeably larger and the black patch on S7 in males is pointed to the apex (not widen as in borneense and the photos in this post). By the way I have not seen it yet.

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