Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
Dorsal and usually lateral faces of femora with fully appressed setae; mesepisternum usually completely lacking erect setae, or with one or two setae near ventral border, rarely with up to five erect setae along posterior border.
Similar species: A. phalangium.
Range
Guatemala, Honduras, El Salvador, Costa Rica (type loc.), Panama. Costa Rica: Atlantic lowlands and cordilleras (distribution map: small, large).
Natural History
This species occurs in wet to moist forest habitats, from sea level to 1400m montane forest (Longino and Cover 2004). Workers are solitary foragers on the forest floor, where they are generalized omnivores, scavengers, and predators on small arthropods. They regularly come to baits of all kinds. Nests are subterranean with an inconspicuous entrance at the soil surface. Colonies maintain multiple empty nests, moving among them (McGlynn et al. 2002, 2003). McGlynn et al. (2002) found a mean colony size of 123 workers (range 55-235). They also found that colonies lacked normal alate queens and instead had ergatoid queens. Colonies usually had one and rarely two ergatoid queens. Alate queens are unknown in the species complex (Longino and Cover 2004).
Longino twice observed the following phenomenon, once in Corcovado National Park with A. phalangium, and once at La Selva Biological Station with A. araneoides. During night collecting, he shined a light on a nest entrance. Workers immediately rushed out of the entrance, each carrying a larva. They ran a few cm from the nest entrance and stopped, then slowly returned to the nest. The exodus from the nest was so rapid that the workers must have been near the nest entrance, already with larvae. It was as though they were waiting at the entrance, ready for a panic evacuation, and set on a hair trigger, such that the smallest stimulus would send them out.
Phil Ward and Alex Wild recently found the first Guatemalan record for the species: Guatemala, El Progreso: 5km W Moraz‡n, 800m. 14¼56«N 90¼12«W; under stone, tropical dry forest, in gully.
Taxonomy
Aphaenogaster araneoides Emery 1890:48, pl. 5, fig. 8. Lectotype worker: Costa Rica [labeled Alajuela, assumed mislabeled, true locality Jimenez] (Alfaro) [MCSN] (examined). Also described as new by Emery 1894:54. Description of male (incorrectly identified as A. phalangium): Emery 1890:47. Description of male: Borgmeier 1949:206. Combination in Aphaenogaster (Ischnomyrmex): Forel 1899:60; in Stenamma: Forel 1907:4; in Aphaenogaster (Deromyrma): Emery 1915:71.
Aphaenogaster (Ischnomyrmex) phalangium var. brevicollis Forel 1899:59. Syntype worker, male: Panama, Volcan de Chiriqu’ (Champion). Combination in Aphaenogaster (Deromyrma): Emery 1921:65. Synonym of araneoides: Longino and Cover 2004:9. Images of syntypes: click here.
Emery (1890) described the first two taxa in the complex. Aphaenogaster phalangium was described first, based on a syntype worker and male from "Alajuela, Jimenez." The worker was described as having a shiny fourth abdominal tergite, and the illustration showed somewhat convex neck and a non-tuberculate propodeum. Aphaenogaster araneoides was described from a syntype worker, also from "Alajuela, Jimenez." It was described as having an opaque gaster, and the illustration shows a tapered neck and a tuberculate propodeum. The published locality data for both species, "Alajuela, Jimenez," is a composite of two collecting localities frequented by Anastasio Alfaro, who sent the material to Emery. Alajuela is a city in the Central Valley of Costa Rica, and is the likely source of the phalangium workers. Jimenez is a small town in the Atlantic lowlands very near La Selva Biological Station, and is the likely source of the A. araneoides workers. The senior author examined the syntypes at MCSN in 1990. Under A. araneoides were (1) a pin with one worker, labeled "Alajuela", and a "Typus" label; and (2) a pin with two workers and an "Alajuela" label. Under A. phalangium were (1) a pin with one worker, labeled "Costa Rica, Alfaro", and with a "Typus" label; (2) a pin with two workers and a "Costa Rica, Alfaro" label, (3) a pin with one worker and an "Alajuela, Alf." label; and (4) a pin with a male labeled "Jimenez." The types were examined before the significance of leg pilosity was understood, and the status of this character was not recorded. However, the worker material under A. araneoides had tapered necks, opaque abdominal tergites, and tuberculate propodeums, while the workers under A. phalangium had convex necks, shiny abdominal tergites, and non-tuberculate propodeums. The MCZC has a pin with two workers, labeled "Ischnomyrma phalangium Em, Costa Rica. from Emery." The specimens and the label look like part of the A. phalangium syntype series, and the specimens have pilose femora. We suspect there were labeling errors, and that all the A. phalangium syntype workers were from one collection from Alajuela, and all the A. araneoides syntype workers and the one A. phalangium syntype male were from one collection from Jimenez. We have requested that the MCSN add labels to these specimens with the suggested corrections. For A. araneoides and A. phalangium we selected the single workers with Emery's "typus" labels as the lectotypes.
Borgmeier's (1949) description of the male was based on two specimens from Hamburg Farm, a site in the Atlantic lowlands of Costa Rica, where A. araneoides is almost certainly the ony species present.
The syntypes of Forel's A. brevicollis come close to bridging the gap between A. araneoides and A. phalangium. The workers are quite robust, there is a row of about five setae on the posterior border of the mesepisternum, the pilosity is abundant and coarse (approaching the more pilose condition of A. phalangium), and the fourth abdominal tergite is smooth and shining. The pilosity on the hind femur is relatively coarse compared to other A. araneoides and yet is clearly appressed on the dorsal surface and strongly contrasting with all known A. phalangium workers.
Literature Cited
Borgmeier, T. (1949) Formigas novas ou pouco conhecidas de Costa Rica e da Argentina (Hymenoptera, Formicidae). Revista Brasileira de Biologia 9, 201-210.
Emery, C. (1890) Studii sulle formiche della fauna neotropica. Bullettino della Societˆ Entomologica Italiana 22, 38-80.
Emery, C. (1894) Estudios sobre las hormigas de Costa Rica. Anales del Museo Nacional de Costa Rica 1888-1889, 45-64.
Emery, C. (1915) Definizione del genere Aphaenogaster e partizione di esso in sottogeneri. Parapheidole e Novomessor nn. gg. Rendiconti delle Sessioni della Reale Accademia delle Scienze dell'Istituto di Bologna. Classe di Scienze Fisiche (n.s.) 19, 67-75.
Emery, C. (1921) Hymenoptera. Fam. Formicidae. Subfam. Myrmicinae. [part] Genera Insectorum 174A, 1-94 + 7 plates.
Forel, A. (1899) Formicidae. [part]. Biologia Centrali-Americana 3, 57-80.
Forel, A. (1907) Formiciden aus dem Naturhistorischen Museum in Hamburg. II. Teil. NeueingŠnge seit 1900. Mitteilungen aus dem Naturhistorischen Museum in Hamburg 24, 1-20.
Longino, J. T., and S. Cover. 2004. A Revision of the Aphaenogaster phalangium complex (Hymenoptera: Formicidae: Myrmicinae). Zootaxa 655:1-12.
McGlynn, T. P., Hoover, J. R., Jasper, G. S., Kelly, M. S., Polis, A. M., Spangler, C. M., and Watson, B. J. (2002) Resource heterogeneity affects demography of the Costa Rican ant Aphaenogaster araneoides. Journal of Tropical Ecology 18, 231-244.
McGlynn, T. P., Shotell, M. D., and Kelly, M. S. (2003) Responding to a variable environment: Home range, foraging behavior, and nest relocation in the Costa Rican rainforest ant Aphaenogaster araneoides. Journal of Insect Behavior 16, 687-701.
Page authors:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
Stefan Cover, Museum of Comparative Zoology, Harvard University, Cambridge MA 02138 USA. scover@oeb.harvard.edu
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