Taxonomy of the Leptogenys chalybaea species group (Hymenoptera, Formicidae, Ponerinae) from Southeast Asia

Leptogenys atra sp. n., L. chalybaea, and L. cyanicatena sp. n. are described from Southeast Asia. These three species are distinguished from other congeners by their eye position and the shapes of the clypeal median lobe and petiolar node. The L. chalybaea species group is proposed based on the similarity of these three species. A key to the species in this group is provided. Colonies of this group contain many ergatoid queens, of which virgin queens do not reproduce, but instead remain in the colony. We believe that they form a multi-purpose caste that can either reproduce or function as helpers. Chain-making behavior for the collective transport of food was confirmed in L. atra and L. cyanicatena. Furthermore, as supporting information, an update key to the Oriental species of Leptogenys is presented.