Gabon, a country of approximately 268,000 square kilometers in Central-West Africa, is a biodiversity hotspot, notably being home to at least 1,100 butterfly species (superfamily Papilionoidea) as documented by Gael Vande Weghe (2010). The country’s remarkable biodiversity can mainly be attributed to its equatorial location and the preservation and remoteness of its ecosystems, particularly its tropical rainforests (Sannier et al. 2016).

Gabon possesses substantial biodiversity potential. As a result, recent studies have revealed numerous new records and species across various taxa. Notable findings include reptiles (e.g., Pauwels et al. 2019), osteichthyan fish (e.g., Sullivan et al. 2016), birds (e.g., Schmidt et al. 2008), Coleoptera (e.g., Bartolozzi et al. 2010), as well as “moths” (e.g., Durante 2012; Bassi 2019). Despite Gael Vande Weghe’s comprehensive work on Gabon’s butterflies in 2010, new species and records will con­tinue to emerge, as exemplified by the recent description of a new Charaxes sp. species : C. cristalensis (Faravel and Bouyer 2022). The ongoing discovery of new species and records in Gabon may be attributed to at least three major factors. First, nearly 300 species may also be found in Gabon, as they are currently known to occur in neighbouring countries (Vande Weghe 2010). Second, extensive unexplored regions within Gabon provide opportunities for additional biodiversity revelations. Third, the presence of specimens in private or institutional collections that have not yet been identified to the species level, or that have not even been scientifically reported, highlights the potential for new discoveries, as exemplified in the current study.

Stempfferia is an Afrotropical genus classified within the Family Lycaenidae; Subfamily Poritiini; and Tribe Epitolini (Jackson 1962). It has undergone thorough taxonomic and phylogenetic revisions (Libert 1999, 2020) and recent descriptions of taxa (Sáfián 2015; Sáfián et al. 2021) resulting in the recognition of 51 va­lid species. These forest species are poorly represented in collections (Vande Weghe 2010; Boireau, comm. pers. 2024). Furthermore, the genus harbours a singular ecology, being associated with arboreal Crematogaster sp. ants (Larsen 2005; Sáfián 2015), so that individuals are prone to be more common in higher layers of the forest, and in the surroundings of “ant-trees”. This implies that areas already “terrestrially” prospected might be inhabited by more Stempfferia species than those already found. This study documents the previously unreported presence of Stempfferia insulana in Gabon.

As (i) the underside of the specimen is not white, the hindwings underside is extensively marked with white and there is no darkened median area separating the discal band from the basal one on the underside of the forewing, this specimen belongs to the S. cercene group. Females of the group are easily distinguishable from males since the suffusion of blue scales of the proximal part of the upper forewings is restricted, and is in great part replaced by white marks (Fig. 1). (ii) There is no obvious black spot on the forewing upperside; (iii) the anal vein is not apparent on the forewing upperside; (iv) the cubital vein of the forewings on the upperside is swollen at its base; (v) the hindwings (upperside) do not have a black margin; (vi) on the upperside, the forewings have androconial scales along about 50% of the anal vein; (vii) the costal margin is not narrowed. This leads to the identification of S. insulana. Other clues to rule out the two sister species, S. cercenoides and S. cercene, occurring in Gabon are as follows. Dorsally, males of S. cercenoides tend to show a slightly lighter blue, and generally about ⅔ of the forewing is blue, while in S. insulana this ratio is about ¾. Males of S. cercenoides have a wing length (i.e., from the apex of the forewing to its insertion in the body) of 16–18 mm, whereas the values known for S. insulana range between 18 and 22 mm. A length of 20.1 ± 0.2 mm was found after several measurements for the Gabon individual. Besides, the underside of S. insulana exhibits finer grayish striations compared to S. cercene, and the presence of a darkish triangle in space 1b is more pronounced and extends further towards the outer margin for most males of S. insulana than those of S. cercene. One might also argue that three other species were recently described in the S. cercene group (Sáfián 2015; Sáfián et al. 2021), but they are not reported from Gabon. Additionally the closely related S. katikae is for the moment only known in the Nimba Moutains (Liberia), far (> 2000 km) from Gabon (Sáfián 2015). Eventually males of S. salonga and S. buea possess a black-streak at the end of the discal cell on the forewing upperside which is not the case for S. insulana males.

To date, S. insulana has been documented in Came­roon (western regions), Equatorial Guinea (Bioko), Congo, Central African Republic, the Democratic Republic of Congo, Uganda, and northwestern Tanzania (Libert 1999, 2020; Williams 2018; Sáfián and Siklósi 2024). An updated distribution map, based on known occurrences, is provided below (Fig. 2). The prior distribution, including its proximity to Gabon, along with the shared characteristics of rainforest ecosystems, provide support for this new record, as previously mentioned by Vande Weghe (2010).

This new record reinforces the value of the examination of biological material in entomological collections.