Eciton vagans angustatum

Identification
Jack Longino:

Minor worker: head, mesosoma, and metasoma maroon, metasoma somewhat lighter; occipital tooth present; petiolar teeth well developed, narrow and acute, flattened, and with ventral carinae extending to variable extent onto posterior face of propodeum, these ventral carinae separate, never fused medially; petiole short and hump-shaped, with prominent anterodorsal flange; fourth abdominal tergite with short, sparse appressed pubescence beneath erect setae.

Major worker: face densely micropunctate, matte; long sickle-shaped mandibles simple, without broad tooth on inner margin; other characters as in minor.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Guatemala, Honduras, Mexico, Panama.

Biology
Jack Longino: This species occurs in dry forest and wet forest habitats. On the Atlantic slope I have not found it above about 800m elevation, but it occurs up to about 1400m (Monteverde) on the Pacific slope.

Raiding is always in columns, never in a carpet like Eciton burchellii. Raiding is almost always nocturnal. In quantitative surveys of Eciton activity at La Selva, angustatum is the only species that is clearly nocturnal, being rarely enccountered during the day and suddenly becoming the most commonly encountered species at night.

Prey of angustatum is largely other ants, and they show a strong predilection for the ponerine genus Odontomachus. I have observed angustatum with Odontomachus prey ten times, out of a total of 28 field observations of columns. They are not strict specialists on Odontomachus, because I have also seen them with Pheidole and Aphaenogaster prey, and once a column came to a blacklight sheet and harvested diverse insects from the base of the sheet.

Castes

 * Worker

Nomenclature

 *  angustatum. Eciton angustata Roger, 1863a: 204 (w.) MEXICO. Wheeler, W.M. 1912e: 207 (m.); Menozzi, 1931d: 188 (q.). Combination in E. (Holopone): Santschi, 1925b: 11. Subspecies of burchellii: Emery, 1900a: 185. Revived status as species: Emery, 1910b: 20. Junior synonym of vagans: Borgmeier, 1939: 405. Revived from synonymy as subspecies of vagans: Borgmeier, 1955: 229. Senior synonym of brunnea: Borgmeier, 1955: 229.
 * brunnea. Eciton brunnea Norton, 1868c: 6 (w.) MEXICO. [Eciton brunnea Norton, 1868a: 62. Nomen nudum.] Junior synonym of rapax: Norton, 1868b: 45; of vagans: Emery, 1910b: 21; of angustatum: Borgmeier, 1955: 229.

Taxonomic Notes
Borgmeier (1955) discussed at some length the subspecies structure of Eciton vagans. He found a disconcerting situation in material from Costa Rica. One queen from the San José area had typical postpetiolar horns, but another collection from near San José and a collection from Hamburg Farm, in the Atlantic lowlands, lacked them. The lack of petiolar horns was unique in Borgmeier's experience and caused him to consider the horned and hornless versions to be two different subspecies, angustatum and Eciton vagans mutatum, respectively. It was disconcerting to him because by most definitions of subspecies they could not be sympatric. He also found a distinction in the males, with angustatum having scutellar furrows indistinct or absent and mutatum having scutellar furrows deep and broad. He also described a small difference in the workers, with angustatum having a pronounced anteroventral postpetiolar tooth and mutatum having the tooth reduced or absent. Eciton vagans angustatum was a previously described taxon, with type locality Mexico, and he described mutatum as a new taxon, with the San José queen as the holotype.

I have not seen any queens of the vagans complex and have not investigated variation in the males. But among the many worker collections I have examined I see considerable variation in the postpetiolar tooth and no indication of discrete character states. Until further evidence to the contrary I consider all Costa Rican material to be one form, E. vagans angustatum. The relationship to E. vagans s. str., from South America, remains uninvestigated.