Formicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Costa Rica, Panama, Colombia (type locality), Trinidad, Brazil (GB, RJ, SP), Paraguay. Costa Rica: throughout country to about 1000m elevation.
Minor worker: Propodeum lacking spines or tubercles of any kind; propodeum somewhat box-like, dorsal and lateral faces flat or nearly flat and meeting at an approximate right angle; dorsal face of propodeum subrectangular; pubescence on first gastral tergite dilute, appressed to suberect, not obscuring integument; color black; propodeum not strongly projecting, forming part of continuous dorsal profile of mesosoma; in face view side of head mostly lacking erect setae, a few setae near mandibular insertion and posterior to eye; dorsal and posterior faces of propodeum meeting at relatively sharp angle; propodeum somewhat elevated.
Similar species: JTL-056.
This species inhabits wet to moist climate areas, in mature forest or second growth vegetation. In lowland sites it can occur in both mature and second growth forest, but at higher elevations is increasingly restricted to open or disturbed habitats. Workers are diurnal. The species is relatively common in canopy fogging samples at La Selva Biological Station.
Nests are in narrow-guage dead stems. Most nests I have encountered have been in stems 4-10mm outside diameter. Nests can be populous: a nest I found in a dead Cecropia petiole lodged in low vegetation contained 319 workers. Nests commonly occur in low vegetation, so the species is frequently encountered and collected.
Prior to this posting I mistakenly identified this species as trapezoideus Mayr. I examined Alex Wild's images of Mayr types and discovered that excisus and trapezoideus have a similar mesosoma shape, but excisus has bare cheeks and trapezoideus has hairy cheeks. The two species are sympatric in parts of South America, judging from some of my own collections from southern Guyana. Click here for Alex Wild type images.
Mayr, G. 1870. Formicidae novogranadenses. Sitzungsber. Kais. Akad. Wiss. Wien Math.-Naturwiss. Cl. Abt. I 61:370-417.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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