Myrmicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Costa Rica: Atlantic slope of Cordillera Volcanica Central from 1500m to 2000m.
Basal margin of mandible flat, without a notch; face with a distinct fan of longitudinal rugae between frontal lobes, and rugose sculpture that extends from mandibular insertions to beyond compound eye; rest of face and promesonotum smooth and highly polished; propodeum shiny and polished like promesonotum, but with variably developed transverse rugae on dorsal face; side of propodeum largely smooth and shining, with at most one longitudinal rugule; dorsal face of propodeum meeting posterior face at an obtuse angle, juncture of two faces smoothly rounded or with a weak transverse carina; legs dark red brown.
Similar species: Stenamma alas, Stenamma expolitum.
This species occurs in cloud forest. Workers have been collected in Winkler samples from the Monteverde cloud forest and from 1500m to 2000m on the Barva Transect in Braulio Carrillo National Park.
I found two nests at Finca Murillo, a 1500m site near the Barva transect. One nest was in a clay hummock sticking up in the middle of a muddy trail through forest. The nest was in a small chamber, about 1 x 2cm, and 15cm deep in the hummock. It contained a dealate queen, a few workers, and brood. The other nest was about 4cm deep in soil beneath leaf litter on the forest floor. The nest was a small, flat-bottomed, hemispherical chamber, about 1cm diameter. The chamber contained 5 adult workers, 1 pharate worker, 19 larger larvae, 3 smaller larvae, and abundant eggs. I did not find a queen.
Unlike its relatives S. expolitum and S. alas, this species does not show a preference for clay banks, and I never found any evidence of special infrastructure at the nest entrance (see S. alas for details).
Longino (2005) reported S. alas occurring to 2000m elevation, but this was based on misidentifications of Stenamma JTL-019 as S. alas. Although the two species are very similar, they have separate elevational ranges and very different nesting habits. On both the Barva transect and in the Pe–as Blancas valley on the east slope of the Cordillera de Tilar‡n S. alas occurs up to about 1100m, while Stenamma JTL-019 occurs at 1500m and above.
Longino, J. T. 2005. Complex nesting behavior by two neotropical species of the ant genus Stenamma (Hymenoptera: Formicidae). Biotropica 37:670-675.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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