Relationships Between Pretarsus Morphology and Arboreal Life in Ponerine Ants of the Genus Pachycondyla (Formicidae: Ponerinae)

Abstract
Morphological traits of the pretarsa, especially the tarsal claws and arolia, of 15 arboreal or ground-dwelling species of the genus Pachycondyla demonstrate that two types of morphologies exist. All of the arboreal and three of the ground-dwelling species have a well-developed arolium in the form of an adhesive pad, whereas the others do not. Moreover, the tarsal claws are spread and horn-shaped in the species of the first group, whereas they are straight and relatively close together in the species without the adhesive pad. The ability to walk upside down is strictly correlated to the presence of the pad. If a large adhesive pad cannot be considered as a morphological adaptation to arboreal life, it, at least, constitutes an indispensable characteristic for the advent of arboreal behavior.