Cyanothemis simpsoni, Libellulidae, is a rarity belonging to a monospecific genus. I am all the more disappointed not to have been able to approach it properly because it exhibits unique characteristics (which makes sense since a genus was created for it) and a striking coloration. Unfortunately, none of these specific details are visible; in particular, the eyes, which touch only at a single point, or the last antenodal crossvein of the hindwing, which is incomplete (which is very rare among Libellulidae, but not unique and nevertheless appears to be inconstant (Fleck, 2004)).
As for the coloration, we were out of luck, and our subject, as apparently happens quite often, did not display the sumptuous blue coloration shown by the subject photographed by K.-D. Dijkstra (among others) on iNaturalist. There is, of course, no relation, but a priori, I do not remember any other odonate displaying such an extent of sky blue as Diphlebia euphoeoides from Oceania.
This coloration in Cyanothemis simpsoni is not due to a bluish pruinescence, as is very often encountered in Libellulidae, but to a subcuticular pigment, which is extremely rare in this family. Among the singularities of this species, one can add the incredible sexual dimorphism; unfortunately, we did not encounter a female, but a few can be found on iNaturalist (photo by Xavier Rufray).
The imago is very close to the genera Rhodothemis and Erythemis, as is the larva (Fleck, 2014). The genus Rhodothemis is present in Indomalaya and Australasia, whereas Erythemis belongs to the New World.
It is difficult to confuse it with another odonate: even in my poor photos, one notes the blue abdomen except for the last two black segments; the same coloration continues between the wings and forms two broad bands on the dorsal surface of the robust thorax, the pronotum, and extends to the large occipital triangle and the frons. The rest of the thorax is very dark. It exhibits a large amber patch at the base of the hindwings and a much smaller one on the forewings.
Ris (1915) measures its abdomen at 29 mm, and it no doubt slightly exceeds 46 mm in total length.
We observed it perched above a small forest stream.
Its distribution extends from Sierra Leone and Guinea to the Democratic Republic of the Congo, with its range broadly covering Cameroon, Gabon, and Congo-Brazzaville.
IUCN Red List.
Etymology of Cyanothemis simpsoni
Cyanothemis, from the Greek kýanos meaning blue, and from Themis. This goddess name has been used, according to Fliedner (2006), more than 50 times to name odonates, particularly Libellulidae, which is only fair since "as the goddess of order, Themis is a very fitting patroness of taxonomists."
Simpsoni; Ris explains, "I have pleasure in naming this beautiful insect after the successful collector of Odonata in Sierra Leone, Dr. J. J. Simpson." This British entomologist traveled through Gambia, Nigeria, the Gold Coast (present-day Ghana), and Sierra Leone in the early 1910s. His main objective was to study the distribution of blood-sucking insects and disease vectors (ticks, tsetse flies, and mosquitoes).
Fliedner, 2006. The scientific names of the Odonata in Burmeister’s "Handbuch der Entomologie"
Günther Fleck (2004). La larve du genre Cyanothemis Ris, 1915 (Odonata : Anisoptera : Libellulidae). Conséquences phylogénétiques, Annales de la Société entomologique de France, 40:1, 51-58.
Ris, F. (1915). New dragonflies (Odonata) of the subfamily Libellulinae from Sierra Leone, W. Africa. Annals & Magazine of Natural History, 15, 213-223, p. 219. [Lien via ADDO]