Solenopsis (Hymenoptera, Formicidae) thief ants in Dominican amber and putative subfossil resin

Solenopsis is a diverse genus of myrmicine ants with a global distribution. Several extinct species have been described but these occurrences are limited to the Palaearctic as imprint fossils. Wilson (1985, 1988) mentioned specimens of Solenopsis preserved in Dominican amber (Middle Miocene, ca. 16 Ma), though these have not been formally described.

Through ethanol exposure and Raman spectroscopy, we assessed the provenance of several putative amber specimens in museum collections. We identified multiple instances of labeled amber specimens that are instead most likely subfossil copal or recent resin – these include specimens in a historical collection. Based on material with provenance and properties consistent with fossil resin, or, amber, we report five new fossil species of minor workers attributed to the genus Solenopsis: S. lamellata sp. nov., S. pilonaria sp. nov., S. merengue sp. nov., S. viralata sp. nov., and S. picapica sp. nov.

One of the species described, S. lamellata sp. nov., is highly aberrant, possessing a spine-like lamella on the posterior margin of the propodeum, a trait not shared with any known Solenopsis species. The discovery of these five fossil species sheds light on the biogeographic history of the genus Solenopsis. Beyond ants, these results highlight the need for caution in assuming the provenance of specimens from museum collections and commercial sources.