The ant genus Lenomyrmex was recently discovered and described from mid to high elevation rainforests in southern Central and northwestern South America. Lenomyrmex currently consists of six described species, which are only rarely collected. Here, we add a new species, Lenomyrmex hoelldobleri sp. n., which was discovered in a stomach content sample of the dendrobatid frog, Oophaga sylvatica, from northwestern Ecuador. Lenomyrmex hoelldobleri can be distinguished from other species in the genus by the presence of a well-developed petiolar node, whereas in all other species the node of the petiole is ill-defined. In addition to the shape of the petiolar node, L. hoelldobleri can be distinguished from the morphologically similar L. costatus by (i) the presence of the metanotal suture, (ii) the direction of the striae on dorsum of propodeum (concentrically transverse in L. hoelldobleri, longitudinal in L. costatus), (iii) the finely striate dorsum of postpetiole, (iv) its larger size, and (v) distinctly darker coloration. We also describe the gyne of Lenomyrmex foveolatus. This collection record from northwestern Ecuador extends the geographic distribution of L. foveolatus 400 km south from its previous record in Colombia. A revised taxonomic key to the workers and gynes of all described Lenomyrmex species is provided. We discuss the taxonomic relationship of L. hoelldobleri to other species in the genus and its biology based on the limited information that is currently available. Finally, we briefly discuss the feeding ecology of dendrobatid poison frogs in the context of providing a valuable source of rarely collected and cryptic new ant species.
