* Trithemis aenea: a new species for Ghana *
Trithemis aenea is one of those extraordinary encounters; our minibus had great difficulty getting out of the ruts on the track due to the unusual January rains, so the first pond on the track was a welcome respite; and what a surprise! No fewer than 3 new species for Ghana, including a very rarely seen one, Urothemis venata. Unfortunately, I didn’t take any photos of this pond, being too engrossed in all these discoveries.
In the field, we were unable to identify this Trithemis, as it was absent from the lists for Ghana. Moreover, the research we were able to conduct in the evening was difficult, with no network or unreliable internet. It was far from us, and the photos were taken with the equivalent of a 300 mm lens.
It was only after returning to France that I had the chance to identify it; it is one of those likely to be encountered in West Africa; Klaas-Douwe Dijkstra shows very few photos on iNaturalist, but this species is one of them!
It was already known from Liberia, Nigeria, Cameroon, Gabon, Congo-Brazzaville, the Democratic Republic of Congo, and neighboring Ivory Coast. Its presence in Ghana is therefore not incongruous.
The IUCN Red List is a little behind ADDO (African Dragonflies and Damselflies Online), which unfortunately disappeared in 2024 and can sometimes be accessed via a Wayback Machine or Web.archive.org.
It is very distinctive among Trithemis with its brown thorax; the pairs of yellow streaks on the abdomen are more common, but the combination of these two criteria is unique in West Africa, especially if one adds the slightly tinted wing apex.
Pinhey tells us it is a large Trithemis (from the stictica group) and that its hindwing measures 32 mm and its abdomen 27 to 28 mm; it measures approximately 40 mm.
On the ADDO website, it states that it thrives in rivers, still waters, and even temporary ponds, in open areas within forests. It appreciates black waters (humic, dystrophic), emergent vegetation, and/or a sandy or soft bottom (like mud). Our observation was made in a roadside pond with a very muddy bottom, and it was perched on an emergent branch; part of the pond was bordered by trees, although it couldn’t truly be called a forest.
As already mentioned, the odonate assemblage was impressive: Urothemis venata and Agriocnemis victoria, two other new species for Ghana, Aethriamanta rezia in large numbers, Trithemis grouti and arteriosa, Crocothemis erythraea, Hadrothemis defecta, and Ceriagrion glabrum.
Etymology Trithemis aenea
Trithemis is composed of the prefix tri, for three, probably because the posterior margin of the pronotum of species in this genus is trilobed, and Themis, who is the goddess of divine law, order, and justice. But why Themis? Certainly because other dragonfly names included names of gods like Echo or Nehalennia, and when Brauer created the genus Trithemis, the fashion was still ‘mythological’. This goddess’s name has been used, according to Fliedner (2006), more than 50 times to name odonates, and rightly so, because ‘as the goddess of order, Themis is a very suitable patron of taxonomists’.
Aenea from the Latin aeneus, an adjective meaning –bronze, and Pinhey writes: « It is named from its bronze coloration« . He also describes « the bronze frons and vesicle », « bronze-brown thorax ». This evolution of the thorax towards a bronze color, which is not observed in any photos on iNaturalist, is probably linked to age.
Fliedner, 2006. The scientific names of the Odonata in Burmeister’s « Handbuch der Entomologie »
Pinhey, 1961 – Dragonflies collected on an expedition from Rhodesia to Nigeria in 1958. Part 1. Entomologists Monthly Magazine, 96, 256-271.