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Eciton of Costa Rica

The genus Eciton is part of the subfamily Ecitoninae, which is comprised of the New World army ants. All known species are nomadic group raiders. Morphologically the subfamily is characterized by having a distinct postpetiole (workers only); eyes absent or composed of at most a single ommatidium (in large workers the ommatidium can be fairly large, but is clearly composed of a single facet); and antennal sockets fully exposed with surrounding semicircular ridges. Workers are weakly to strongly polymorphic.

Ecitonine males are robust insects with elongate, cylindrical abdomens, and are often encountered at lights. They are strong fliers, and superficially resemble wasps. When captured and held in one's fingers, they make probing motions with the abdomen, as though imitating stinging motions of vespid wasps. They have large and heavily sclerotized genitalia, which are taxonomically useful for distinguishing genera and species. Queens are permanently wingless, always remain in colonies (reproduction is by colony fission), and are rarely seen.

The last synthetic revision of the New World army ants was Borgmeier (1955). This is a large work, in German, with over 700 text pages and 87 plates of figures. Watkins ((1976) provided a useful synopsis, with species lists, English translations of the keys, distribution maps, and compressed versions of the figures. Additional information on army ants can be found at Gordon and Roy Snelling's army ant pages, a site dedicated to New World army ants.

In Costa Rica there are four genera of army ants: Eciton, Labidus, Neivamyrmex, and Nomamyrmex. Eciton contains the largest army ants, and the most conspicuous. Workers are strongly polymorphic. The tarsal claws are distinctly toothed (distinguishing Eciton from Neivamyrmex); there are small but distinct spines or flanges on the posterodorsal margin of the propodeum (distinguishing Eciton from Labidus); and the scapes are relatively long and thin (distinguishing Eciton from Nomamyrmex). The soldiers have greatly enlarged, fish hook-like mandibles, which no other army ants have.

The trend over the past 50 years of ant taxonomy has been to eliminate the rank of subspecies, either raising subspecies to species or synonymizing them. But army ants show geographic patterns of character variation that lend themselves to subspecies recognition. Major structural differences in body shape and male genitalia separate major lineages with broad geographic ranges, while within those lineages more superficial characters such as color, pilosity patterns, or sculptural elements show a mosaic of discrete parapatric forms. The variation is not intrapopulational, nor is it a gradual continuum of geographic variation, sensu Mayr's polytypic species. The early ant taxonomists (e.g. Emery, Forel) made small phylogenetic statements by giving these geographic variants formal taxonomic names as subspecies or varieties. Borgmeier followed that tradition. The keys in Watkins do not include subspecies, but the taxon lists and distribution maps do. When relevant, this website retains subspecies status of Costa Rican taxa.

Literature Cited

Borgmeier, T. 1955. Die Wanderameisen der neotropischen Region. Studia Entomologica 3:1-720.

Watkins, J. F., II. 1976. The identification and distribution of New World army ants (Dorylinae: Formicidae). Baylor University Press, Waco, Texas.

Page author: John T. Longino longinoj@evergreen.edu

Date of this version: 16 July 2005.

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