Eciton

Eciton comprises the most conspicuous army ants in the New World. The huge colony size combined with epigaeic nesting and foraging habits makes these ants major invertebrate predators and key species of the tropical ecosystems.

Identification
Diagnosis. Worker. Eciton is recognized by a combination of 12-segmented antennae, propodeal spiracle high on the propodeum, propodeal declivity armed with cuticular tubercles or lamellae, binodal waist, pretarsal claws armed with a tooth and presence of a prominent metatibial gland visible as an elongate patch of whitish or yellowish cuticle on the flexor (inner) surface of tibia. Among New World army ants, Eciton is similar to its closest relative Nomamyrmex, with which it shares propodeal armament, but workers of all sizes are easily separated by a conspicuous white stripe on inner hind tibiae that is absent in Nomamyrmex. Labidus species can be distinguished from Eciton by their smooth, unarmed propodeum.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
Eciton is the best studied lineage of the dorylines, owing to the lifetime efforts by pioneers of army ant biology, including Thomas Schneirla, Thomas Borgmeier and Carl Rettenmeyer. Among the twelve described species, Eciton burchellii has attracted the most attention, followed by E. hamatum, although most species have been at least briefly observed in the field. Most accounts of Eciton biology are based on the two well-known species. The literature on Eciton is vast, and it is impossible to cite all of the even more significant original contributions. Good overviews of Eciton biology can be found in Rettenmeyer (1963), Schneirla (1971), Telles Da Silva (1977a, 1977b), Rettenmeyer et al. (1983) and Gotwald (1982, 1995). The account below is based on these sources, unless noted otherwise. The life of an Eciton colony can be summarized as follows. The colony alternates between the so-called statary and nomadic phases. The cycles are understood to be regulated by brood development rather than an endogenous rhythm in adult ants. During the statary phase a single queen is laying eggs and the brood inside the nest consists of pupae and eggs; foraging does not happen every day and raids are relatively much less intensive. There are no emigrations to new nesting sites. In the nomadic phase, the queen stops producing new eggs and her abdomen contracts; the colony contains many developing larvae that need nutrition. Raids and emigrations usually occur every day. In Eciton burchellii, the statary phase lasts on average 20 days and the nomadic phase is 14 days long. A mature colony containing a single mated queen will eventually produce up to six virgin queens and hundreds to thousands of males, depending on the species. Usually the queen that emerges first leaves the colony with workers clustered around her. She has the best chance to survive and lead the fissioning part of the nest. About half of the workers eventually leave with the virgin queen. Because the colony is divided into approximately equal halves, the workers represent a substantial part of the reproductive investment. This explains the highly male-biased sex ratio, also typical of other social insects with colony fission (Pamilo 1991). The older, mated queen emigrates together with brood while the virgin queen disperses with the remaining workers. Shortly after the fission, the colony will accept multiple males that enter the bivouac. The males must first be accepted by the workers and they lose their wings before mating. Each male can mate only once, but E. burchellii queens are known to mate with a dozen males on average, this mating frequency being among the highest in eusocial Hymenoptera (Kronauer et al. 2006). Although mature colonies have been observed to occasionally admit new males, there is strong evidence that all of the mating occurs when the queen is young (Kronauer and Boomsma 2007a). A fertilized queen can produce up to 225,000 eggs per 35-day cycle and 14 million eggs during her lifetime (Schneirla 1971, Kronauer and Boomsma 2007a). Colony structure and nesting behavior has been studied in some detail in several species. Temporary nests are made up of bodies of workers, hanging together by their legs from a supporting structure. These bivouacs can be found in a variety of microhabitats, but common nesting sites include hollow logs, spaces between buttresses of large trees, and empty soil cavities such as abandoned mammal burrows. Eciton species vary in their preferences for bivouac sites, with E. burchellii and E. hamatum nesting in exposed sites, the former often hanging above ground without touching the surface. Eciton dulcius and E. mexicanum are known to nest only in underground cavities, and E. vagans is intermediate, sometimes found in relatively exposed sites, but often nesting under logs and in rock crevices. Colony size estimates vary widely and reliable data exists only for E. burchellii and E. hamatum. Rettenmeyer estimated that mature colonies of E. burchellii contain from 300,000 to 700,000 worker ants before fission and 100,000 to 500,000 for E. hamatum. Colony densities have been estimated in several localities for Eciton burchellii, ranging from 3.5 colonies per 100 ha on Barro Colorado Island, Panama, to 11 colonies in Corcovado, Costa Rica (Franks 1982, Vidal-Riggs and Chaves-Campos 2008).

Nomenclature

 *  ECITON [Ecitoninae: Ecitonini]
 * Eciton Latreille, 1804: 179. Type-species: Formica hamata, by subsequent designation of Shuckard, in Swainson & Shuckard, 1840: 173.
 * Eciton senior synonym of Camptognatha, and material of Ancylognathus (nomen nudum) referred here: Smith, F. 1855c: 160.
 * Eciton senior synonym of Mayromyrmex: Emery, 1906a: 718.
 * Eciton senior synonym of Holopone: Borgmeier, 1936: 55.
 *  ANCYLOGNATHUS [Nomen nudum]
 * Ancylognathus Lund, 1831a: 121, 135. Type-species: Ancylognathus lugubris. Nomen nudum.
 * Ancylognathus material referred to Eciton: Smith, F. 1855c: 160.
 * CAMPTOGNATHA [junior synonym of Eciton]
 * Camptognatha Gray, G.R. 1832: 516. Type-species: Camptognatha testacea (junior synonym of Formica hamata), by monotypy.
 * Camptognatha junior synonym of Eciton: Smith, F. 1855c: 160.
 * HOLOPONE [junior synonym of Eciton]
 * Holopone Santschi, 1925b: 11 [as subgenus of Eciton]. Type-species: Eciton rapax, by original designation.
 * Holopone junior synonym of Eciton: Borgmeier, 1936: 55.
 * MAYROMYRMEX [junior synonym of Eciton]
 * Mayromyrmex Ashmead, 1905b: 381. Type-species: Labidus fargeavii (junior synonym of Atta quadriglumis), by original designation.
 * Mayromyrmex junior synonym of Eciton: Emery, 1906a: 718.