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Brown (unpublished) lists southern Mexico to mountains of Peru and northeast Brazil. Kempf (1972) lists Costa Rica, Colombia, Ecuador, Venezuela, Peru, Bolivia, Trinidad, Guianas, Brazil (AM, PA, CE, GB, RJ, SP). Costa Rica: Atlantic lowland wet forest to 800m; southern Pacific lowland wet forest to 1200m at Wilson Botanical Gardens near San Vito.
Ponera (Pachycondyla) impressa Roger 1861:6. Syntype worker: Colombia.
Pachycondyla fuscoatra r. transversa Emery 1890:58 (part). Syntype workers: Alajuela, Juan Vinas [MCSN] (examined). Syntypes recognized as mixed series by Emery (1901). Synonymized under P. impressa by Kempf 1961:195. Proposed lectotype: Alajuela queen.
Emery first included specimens from Alajuela and Juan Vinas in his description of transversa, and later reidentified the Juan Vinas specimens as Forel's purpurascens (Emery 1901, 1911). At the Emery collection in Genoa no material is clearly marked as the type of transversa, but there is a queen labeled "Alajuela" under transversa and two workers labeled "Juan Vinas" under purpurascens. I assume these specimens are the syntypes. The queen from Alajuela should be designated lectotype.
Currently there are 5 names synonymized under impressa (Kempf 1961, Bolton 1995):
andicola Santschi 1913. Ecuador.
cearensis Forel 1901. Brazil.
inca Emery 1901. Peru.
montana Forel 1912. Colombia.
purpurascens Forel 1899. Costa Rica.
transversa Emery 1890. Costa Rica.
I consider purpurascens to be a distinct species (see discussion under purpurascens).
I have briefly examined specimens of the impressa complex from various sites in South America, and the features that distinguish impressa and purpurascens in Costa Rica do not remain constant elsewhere. Thus the global definition of impressa is problematic. If further research resolves impressa into multiple species elsewhere in its range, and the Costa Rican form proves distinct from impressa s.s., transversa will be the correct name to apply.
This species is relatively rare, compared to the similar and much more abundant P. harpax. Foragers occur on the forest floor, and are never arboreal.
I have observed one nest of impressa. In Corcovado National Park, I put dead tabanids on the ground in an area with scattered impressa workers. One picked up a tabanid and I tried to follow it, but it was easily disturbed, and it would constantly hide motionless under leaves. I eventually found a nest entrance in the center of a mud clump. The nest went horizontally back into a clay bank, a short distance to a gallery about 2cm broad and 1cm high.
Bolton, B. 1995. A New General Catalogue of the Ants of the World. Harvard University Press, Cambridge, Mass.
Emery, C. 1890. Studi sulle formiche della fauna neotropica. I-V. Bullettino della Societa Entomologica Italiana 22:38-80.
Emery, C. 1901. Notes sur les sous-familles des Dorylines et Ponerines (Famille des Formicides). Annales de la Societe Entomologique de Belgique 45:32-54.
Emery, C. 1911. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 1181-125.
Kempf, W. W. 1961. As formigas do genero Pachycondyla Fr. Smith no Brasil (Hymenoptera: Formicidae). Revta Bras. Entomol. 10:189-204.
Kempf, W. W. 1972. Catalogo abreviado das formigas da Regiao Neotropical. Studia Entomol. 15:3-344.
Roger, J. 1861. Die Ponera-artigen Ameisen (Schluss). Berl. Entomol. Z. 5:1-54.
Found most commonly in these habitats: 19 times found in tropical moist forest, 13 times found in wet forest, 11 times found in montane wet forest, 9 times found in tropical wet forest, 7 times found in 2º lowland rainforest, 8 times found in 2º wet forest, 5 times found in montane rainforest, 5 times found in tropical rainforest, 3 times found in mature wet forest, 2 times found in lowland wet forest, ...
Collected most commonly using these methods or in the following microhabitats: 35 times Baiting, 19 times MiniWinkler, 18 times Search, 9 times MaxiWinkler, 9 times Pan Trap, 5 times Winkler, 3 times flight intercept trap, 1 times fogging, 1 times Mini Winkler, 1 times yellow pan trap
Elevations: collected from 5 - 1600 meters, 554 meters average