Upon seeing Pseudagrion perfuscatum (Coenagrionidae), I immediately thought of a species I have encountered at least three times in Asia, Pseudagrion pruinosum (here in Thailand). I am not the only one, as F. F. Laidlaw (among others), a famous odonatologist and describer of many species, was also a victim of this confusion (1), but the anal appendages are slightly (but undoubtedly) different.
Laidlaw describes in detail the differences in thoracic colouration, and I must say they leave me sceptical and do not seem to apply to our specimens, which are very similar in this respect. What is very evident in my photos and mentioned by this author is that the last segments of Pseudagrion perfuscatum are never covered with this whitish pruinescence, and therefore the red ring or red dots on the ninth segment are always visible, whereas they are simply absent in P. pruinosum. Be that as it may, it is accepted that P. pruinosum is not present in Borneo (present in Singapore).
Its abdomen measures 30 to 33 mm, including appendages, so it measures about 39 mm. It is smaller than P. pruinosum, which is given as 40 to 44 mm (2).
Above is a younger specimen, whose upper side of the thorax is not yet covered with pruinescence. Note the red postocular spots and the dull red face, whereas that of P. pruinosum is orange or bright red (here in Vietnam).
Habitat et distribution géographique
We encountered it on a wide river surrounded by forest, the Timuoh River; it had chosen a well-cleared area along the bank, a zone invaded by low vegetation. It turned out to be difficult to approach, and despite the time I spent near it, I managed few photos.
It is endemic to Borneo, where it is reportedly absent only from eastern Sabah.
IUCN Red List.
Eymology de Pseudagrion perfuscatum
Pseudagrion (3) from Ancient Greek pseudo – false, erroneous, and agrion, this, as Selys (1876) wrote, to demonstrate the difficulty of separating this genus from Agrion; "the Pseudagrions seem very close to the true Agrions." Agrion, from the Greek agrios – wild, living in the fields.
Perfuscatum from the prefix per- meaning completely, entirely, and from fuscare meaning to darken, to blacken, undoubtedly due to the fact that the dorsal side of the thorax remains dark brown, whereas that of P. pruinosum becomes covered with pruinescence: "Even in very old males the upperside of the thorax of perfuscatum always remains brown, ..." (1).
1- Lieftinck, 1937 – Descriptions and records of South–east Asiatic Odonata. Treubia 16: 55–119. P. 94.
2- Robin Ngiam & Marcus Ng - A photographic guide to the Dragonflies and Damselflies of Singapore - John Beaufoy Publishing – 2022
3- The Naming of Australia’s Dragonflies, Ian Endersby & Heinrich Fliedner, Busybird publishing.