Panama, Honduras, Guatemala
This species occurs in moderately seasonal to aseasonal wet forest, from sea level to 2000 m elevation. All recent specimens are from Winkler or Berlese samples of sifted leaf litter. It is rare for ant species to occur across such a broad elevational spectrum, and given the considerable variability in setal pattern and wide geographic range, it may comprise multiple allopatric populations with unknown degrees of genetic divergence. In Honduras it was a rare cloud forest species at Comayagua and La Muralla and a rare lowland species along the north Caribbean coast. At La Union, in the mountains southeast of Zacapa, Guatemala, it was a rare species sympatric with the much more abundant R. megisthmica. In cloud forest on the slopes of Volcán Atitlán in western Guatemala it was abundant—occurring in 29 of 100 miniWinkler samples—and sympatric with the smaller R. atitlanica.
Worker. HW 0.58–0.68 (n=13); mandible with three teeth on masticatory margin, middle tooth largest; subapical tooth with distinct reclinate denticle at base; subapical tooth about twice as long as apical tooth; intercalary teeth prominent, one closest to apical tooth about half as long as apical tooth; labrum trapezoidal, anterior lobes triangular, inner margins of lobes shallowly sloping to semicircular median notch; propodeal tooth acute to right-angled, infradental lamella evenly and shallowly concave; squamiform setae abundant on first gastral tergite, either uniformly covering entire tergite or covering varying extent of posterior portion, at least posterior half with abundant setae. The queen and male are unknown.
Note added 1 March 2013: Longino and Boudinot (2013) redescribed R. isthmica and included it in the key without examining types or any other material from Panama. Longino examined Panama material from the Kaspari lab, collected near the type locality. Although closest to the concept of R. isthmica in Longino and Boudinot, it is different enough to key incorrectly. The Panama material has three primary differences from the Guatemala/Honduras material examined by Longino and Boudinot: (1) the labrum has longer lobes and deeper medial sinus (causing the key to fail at couplet 4); (2) the mandible has more teeth on the masticatory margin proximal to the reclinate denticle on the subapical tooth, two basal teeth, a denticle, a large tooth, and another denticle; and (3) the infradental lamella is broad and with a secondary convexity beneath the tooth. The Guatemala/Honduras material, apparently allopatric with the Panamanian R. isthmica (none are known from Costa Rica and Nicaragua), is thus an undescribed species incorrectly identified as R. isthmica in Longino and Boudinot (2013).
Holotype worker: Panama, Barro Colorado Island, 29 July 1938 (E. C. Williams, Jr. No.313(131))
Found most commonly in these habitats: 42 times found in cloud forest, 6 times found in tropical rainforest, 1 times found in 2º lowland tropical rainforest, 1 times found in mesic hardwood forest, 1 times found in oak forest, 1 times found in forest floor, 1 times found in oak, pine, Liquidambar forest
Collected most commonly using these methods or in the following microhabitats: 37 times MiniWinkler, 12 times MaxiWinkler, 2 times Berlese
Elevations: collected from 190 - 2010 meters, 1417 meters average