Dolichoderinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Additional images:
Queen, mandible (small, large), petiole, lateral view (small, large, original line drawing, reduced line drawing).
Worker, petiole, lateral view (small, large).
Range
Panama, Costa Rica, Guatemala. Costa Rica: widespread.
Identification
Queen
Measurements (n=5): HLA 1.55 (1.48-1.64), HW 1.09 (1.05-1.17), SL 0.76 (0.74-0.79), CI 71 (70-73), SI 50 (48-51).
Palpal formula 5,3; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible coarsely punctate, puncta bearing stiff erect setae, mandible appearing bristly; medial and lateral clypeal lobes at about same level; head subrectangular, posterior margin weakly excised medially; petiolar node short, broadly triangular; posteroventral petiolar lobe strongly convex from front to back; scape with sparse and inconspicuous erect setae, about as long as one third maximum width of scape; hind tibia with short inconspicuous suberect setae, longest of these about as long as one sixth maximum width of tibia (MTSC 5-10); side of head with 0-2 short setae near mandibular insertion, setae lacking elsewhere, posterior margin of head with sparse erect setae; pronotum with posterior row of erect setae; mesoscutum and scutellum with very sparse erect setae; propodeum with a few erect setae on sides, none on dorsomedial area; petiolar node with rim of whitish erect pubescence, a few longer erect setae on lower sides but in profile with none projecting above apex, posteroventral lobe with abundant long setae; gastral terga with very sparse erect setae; general body color dark brown, the following lighter yellow brown: thin strip of anterior clypeus and area near mandibular insertions, thin anterior and posterior bands on gastral terga, gastral sterna.
Worker
Measurements (n=4): HLA 1.31 (1.04-1.42), HW 1.09 (0.92-1.20), SL 0.73 (0.67-0.77), CI 84 (83-88), SI 56 (54-64).
Palpal formula 5,3; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible with abundant piligerous puncta, surface between puncta smooth and shining, variable extent of base faintly microareolate; medial and lateral clypeal lobes at about same level; head subquadrate with weakly convex sides, moderately excavate posterior margin; in lateral profile mesosoma compact, pronotum and mesonotum nearly forming a single convexity, with promesonotal suture very weakly impressed; scape with sparse, inconspicuous erect setae, length of setae about one half maximum width of scape; outer surface of hind tibia with a row of about 5 very short, inconspicuous, suberect setae; side of head lacking erect setae or with 1-2 near mandibular insertion; posterior margin of head with sparse erect setae; pronotum and mesonotum with sparse erect setae, dorsal face of propodeum lacking erect setae; color red brown.
Similar Species
The bristly mandibles ally this species with A. forelii and A. brevis. Queens of A. nigricans are smaller than queens of A. forelii. Queens of A. brevis have shorter scapes than queens of A. nigricans (SI 39-43 versus 50-52, respectively). Workers of A. brevis are distinguished from workers of A. nigricans by the reduced number of setae on the hind tibia, 0-2 on A. brevis versus > 5 on A. nigricans.
Natural History
Longino (1996) reviewed the taxonomy and biology of this species. It is found in wet forest habitats, where it nests in live stems of a wide variety of trees, including Cecropia insignis, Inga, Pentaclethra macroloba, Erythrina poeppigiana (Fabaceae), Tetrathylacium costaricensis, Licania, Phoebe chavarriana (Lauraceae), and Dendropanax arboreus (Araliaceae). At La Selva Biological Station, workers were encountered in two of 18 Project ALAS canopy fogging samples, from crowns of Carapa guianensis (Meliaceae) and Tapirira guianensis (Anacardiaceae).
The workers make small holes in shoot tips of live trees, leading to irregular cavities containing brood. The walls of the cavities are lined with abundant coccoid Hemiptera. As flushes of new growth occur, the ants move into the new shoots and progressively abandon older chambers lower in the branch. Colonies are polydomous, with brood distributed in multiple nests. Colonies can be large, occurring in large portions of large canopy trees. In contrast to the similar species A. brevis, workers do not use carton construction and often have exposed foragers on stems. Although new alate queens are often dispersed in the nests of a colony, I have never found a physogastric colony queen. This suggests that colonies are monogynous, with the colony queen hidden in one of the many nests that occur in tree crowns. Brood must be transported externally to new nests.
Comments
In Longino (1996), two morphospecies, JTL-001 and JTL-002, were considered close to or conspecific with A. nigicans. The former was discovered to be A. brevis, and the measurements of the latter cluster with the holotype queen of A. nigricans. The separateness of A. brevis and A. nigricans was further supported when the two species were found to be sympatric. I found both species nesting in the canopy of a large Licania tree in Corcovado National Park. At the time I did not understand the species boundaries, but in the field I observed behavioral differences. In my field notes I commented that Azteca high in the crown produced a black crusty carton on the stem surfaces and were rarely seen exposed on the surface, while another group of Azteca lower in the crown looked similar but did not make carton and were active and exposed on the surface of the live stems in which they nested. The former were A. brevis and the latter A. nigricans.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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