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The New World army ants are in the subfamily Ecitoninae. This site is intended primarily as an identification guide to Costa Rican species, and no attempt is made to summarize the biology of army ants or cover them at a larger spatial scale. 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. Neivamyrmex can be distinguished from the other genera by the structure of the tarsal claws. Neivamyrmex claws are simple, while the claws of the other three genera have a second tooth (Figure). Other characters of Neivamyrmex are a lack of propodeal spines and weak polymorphism (there can be extensive size variation, but no dramatically enlarged and modified soldiers).
At this point the Neivamyrmex species list contains species based on both workers and males, but the key is only for workers, and the species accounts are under construction for species known from males only.
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.
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.
An important characteristic of army ants that is important for taxonomy and species identification is that they have large, conspicuous males with elaborate and complex morphology. These conspicuous males often fly to lights and some are routinely found in Malaise trap samples. An entire taxonomy has been created based on males alone, using characters of the head and genitalia. In contrast, workers are collected by walking trails and looking for foraging columns, and a parallel taxonomy has been created based on worker morphology. It is very difficult to find workers and males together, and there are no clues in the morphology to suggest which males go with which workers. Males and workers have been associated for the most conspicuous and abundant army ants, but for the majority of species these associations have not been made. Thus we can anticipate an unstable taxonomy for a while as associations are made and synonymies established.
Neivamyrmex are the least conspicuous but most diverse of the Costa Rican army ants. At low elevations there is only one species, N. pilosus mexicanus, that is a relatively common and conspicuous diurnal forager. At higher elevations, N. sumichrasti is a moderately abundant diurnal forager. All the rest are either low density nocturnal surface foragers or entirely subterranean. It is very difficult to sample these in any quantitative fashion. Long hours walking trails at night will yield the occasional Neivamyrmex collection from a raiding column. Subterranean species are sometimes found by turning stones, or they may briefly surface to cross a hard-packed footpath.
Many of the identifications in the website are very tentative. They are based on my attempt to use Borgmeier's keys and geographic data, and I have not examined any type material. Users of the keys and species accounts should thus be warned of the tentative nature of some of the identifications, and I encourage my colleagues to suggest corrections.
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: 14 July 2005.
