Acisoma trifidum (Libellulidae) comes as a small surprise, as I did not expect it to be so different from the other Acisoma species I had encountered in Africa, namely A. inflatum and A. variegatum, or even the one I know best from frequently encountering it in Asia, Acisoma panorpoides. In all my photos, the distal part of the abdomen is strongly upturned; none of the Acisoma species I had the fortune of encountering, in Asia or Africa, exhibited this characteristic. I have gone through a number of documents to write this article, and none of them mention this detail...
Based on Mens, L.P., Schütte, K., Stokvis, F.R. & Dijkstra, K.-D.B. (2016), the genus Acisoma comprises six species: one Asian, Acisoma panorpoides, and five African ones, of which two, A. attenboroughi and A. ascalaphoides, are strictly limited to Madagascar. Until then, only two species were recognized: A. ascalaphoides in Madagascar and A. panorpoides from the rest of Africa to Asia.
But Acisoma trifidum is undoubtedly the easiest to isolate and identify due to the contrast between its very pale abdomen and its dark thorax crossed by a series of short yellow lines, its dark face, and its black labrum and labium marked with white spots, with the black extending to cross the eye.
Kirby, in 1889, had noticed venation anomalies between Asian and African subjects, in particular the fact that African subjects exhibited an incomplete last antenodal crossvein: "There are several doubtful forms from Africa and Madagascar, in all of which (with the exception of a specimen which I regard as the true A. ascalaphoides of Rambur) the last antenodal is not continuous." And indeed, all African Acisoma exhibit this characteristic, which is less absolute for A. ascalaphoides (with only 89% of subjects). And in the same document, further on, he describes Acisoma trifida, which international nomenclature has transformed into trifidum.
According to Kirby, the total body length is 26 mm.
It is found throughout West and Central Africa, from Senegal to Uganda, Rwanda, and northern Zambia.
IUCN Red List.
It favors more forested ponds than those of A. inflatum, with which it frequently coexists. We found it at the forest edge, then at a very small pond in an open area (Ankasa Forest Reserve Lodge), and at a larger swampy pond—these last two bodies of water being in open areas!
It is certainly less common than the latter in the areas we explored; we did not observe any females.
Etymology of Acisoma trifidum
Acisoma, from the Greek akis meaning needle or arrow and sôma meaning body, in reference to the shape of the abdomen, which is dilated at the base and tapers toward the end.
Trifidum, from the Latin adjective trifidus, meaning divided into three. Kirby indeed noted that this Acisoma trifidum presented three cells in the subtriangle of the forewing, whereas the Asian species and those of mainland Africa showed only one. He was unaware that in 40% of cases it only comprises two (this number can vary from one wing to the other, as shown by the subject below).
In English, it is called the Pied Pintail, a rather evocative name that refers to its black-and-white (pie/pied) coloration and its tapered tail.
Kirby, 1889 - A revision of the subfamily Libellulinae, with descriptions of new genera and species. Proceedings of the
Zoological Society of London - 12 (9), 249–348.
Mens, L.P., Schütte, K., Stokvis, F.R. & Dijkstra, K.-D.B. (2016) - Six, not two, species of Acisoma pintail dragonfly (Odonata: Libellulidae) - Zootaxa, 4109 (2), 153–172.
Acisoma trifidum male, Ghana, Amasuri Conservation Area, 15/01/2026
Kirby, 1889 - A revision of the subfamily Libellulinae, with descriptions of new genera and species. Proceedings of the
Zoological Society of London - 12 (9), 249–348.
Mens, L.P., Schütte, K., Stokvis, F.R. & Dijkstra, K.-D.B. (2016) - Six, not two, species of Acisoma pintail dragonfly (Odonata: Libellulidae) - Zootaxa, 4109 (2), 153–172.