Eciton mexicanum

Identification
Jack Longino:

Minor worker: head and mesosoma maroon, metasoma somewhat lighter yellow brown; occipital tooth present; petiolar teeth fused, forming a bilobed scoop-like structure, with a single median carina extending down the posterior face of propodeum; petiole long and low, subrectangular, occasionally with a low anterodorsal rim; fourth abdominal tergite with short, sparse appressed pubescence beneath erect setae.

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

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Guatemala, Honduras, Mexico, Panama, Paraguay, Peru, Venezuela.

Biology
Baudier et al. (2015) studied thermal tolerances of a variety of army ant workers. Eciton mexicanum was one of a number of army ant species sampled with a life history that includes both below and above ground activities.

Jack Longio: This species can be found in dry forest or wet forest, from sea level to montane areas.

Raiding is always in columns, never in a carpet like Eciton burchellii. Many of the raiding columns I have observed have been at night, showing a tendency to be nocturnal, but I also encounter columns during the day. The few times I have encountered prey they have been large ponerines in the genera Ectatomma and Pachycondyla and relatives.

O'Donnell et al. (2020) report this species foraging both day and night.

Castes

 * Worker


 * Soldier


 * Male

Nomenclature

 * . Eciton mexicana Roger, 1863a: 205 (w.) MEXICO (no state data).
 * Type-material: syntype workers (number not stated).
 * Type-locality: Mexico: (no further data).
 * [Note: locality provided by Borgmeier, 1955: 257, Mexico: Chiapas, Escuintla, 3-4.iv.1945 (Schneirla), is not based on type-material and is not the type-locality.]
 * Type-depository: MNHU.
 * Emery, 1894c: 178 (s.); Borgmeier, 1933a: 92 (q., as rogeri); Borgmeier, 1955: 252 (m.).
 * Status as species: Roger, 1863b: 36; Mayr, 1863: 459; Mayr, 1865: 77 (in key); Norton, 1868a: 62; Norton, 1868b: 45; Norton, 1868c: 7; Mayr, 1886b: 117 (in key); Emery, 1890b: 38; Dalla Torre, 1893: 4; Emery, 1894c: 178; Emery, 1894k: 45; Emery, 1896g: 33; Forel, 1899c: 27; Smith, M.R. 1931a: 16; Borgmeier, 1955: 250 (redescription); Kempf, 1961b: 486; Kempf, 1970b: 323; Kempf, 1972a: 102; Watkins, 1976: 9 (in key); Watkins, 1982: 209 (in key); Bolton, 1995b: 185; Palacio, 1999: 151 (in key); Wild, 2007b: 25; Branstetter & Sáenz, 2012: 254; Bezděčková, et al. 2015: 109; Palacio, 2019: 601.
 * Senior synonym of rogeri: Borgmeier, 1955: 250; Kempf, 1972a: 103; Bolton, 1995b: 185.
 * Distribution: Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Guatemala, Mexico, Paraguay, Peru.
 * Current subspecies: nominal plus argentinum, goianum, latidens, moralum, panamense.
 * rogeri. Eciton rogeri Dalla Torre, 1892: 89.
 * Unnecessary replacement name for mexicanum Roger, 1863b: 205.
 * Status as species: Dalla Torre, 1893: 6; Emery, 1894c: 178; Emery, 1896h: 625; Forel, 1899c: 25; Emery, 1900a: 185; Wheeler, W.M. 1907a: 271; Emery, 1910b: 21; Forel, 1911c: 288; Mann, 1916: 420; Borgmeier, 1923: 40; Bruch, 1934b: 125; Borgmeier, 1939: 406.
 * Junior synonym of mexicanum: Borgmeier, 1955: 250; Kempf, 1972a: 103; Bolton, 1995b: 186.

Taxonomic Notes
Jack Longino:

Borgmeier (1955) described a subspecies Eciton mexicanum panamense from central Panama, based on workers and queen. He differentiated panamense from mexicanum s. str. as follows (my translation): "The soldier differs from mexicanum s. str. by the shorter scapes (1.84mm), shorter funiculus, shorter mandible (3mm) and smaller postpetiole (0.56mm broad posteriorly), and by a well developed anteroventral petiolar tooth (also present on the available minor workers, while it is missing or very short on the workers of mexicanum s. str.)." His key to the queens differentiated the forms as follows:

Petiolar horns with approximately parallel sides, dorsal longitudinal sulcus broad and deep: mexicanum s. str.

Petiolar horns tapered posteriorly, dorsal longitudinal sulcus narrow and shallow: panamense.



The degree of development of the anteroventral petiolar tooth is highly variable among the Costa Rica material I have examined, from nearly absent to well developed. I consider panamense a junior synonym of mexicanum until evidence to the contrary.

References based on Global Ant Biodiversity Informatics

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