Eciton burchelli
army ants

Eciton burchelli is found in the tropical regions of Central and South America. (Holldobler and Wilson, 1990)

Eciton burchelli are terrestrial, although colonies may occasionally bivouac (temporarily nest) in trees several meters above ground. Army ants need very humid, warm climates. Although they may venture out to forage in open or agricultural areas, they prefer heavily forested environments. (Akre, 1968; Franks, 1982; Holldobler and Wilson, 1990)

Eciton burchelli are polymorphic, worker sizes range from 3mm to 12mm. They have long, pointed, falcate (hook-shaped) mandibles. Their long legs on an elongated body make them appear almost spider-like. On their feet are tarsal hooks, which they use to grip each other as they form bridges and bivouacs. They range from a deep golden color to a dull brown. Workers have single faceted, compound eyes, double segmented waists, and a well-developed sting. (Franks, 1982)

Eggs are laid by the queen and are then taken away and arranged throughout the center part of the bivouac. At the same time, the larvae from the previous cycle begin to pupate, spinning silken cocoons for themselves. Once enclosed in their cocoons, they are placed on the outer edges of the bivouac to metamorphose. After metamorphosis is complete, new adults need help from other colony members to eclose (emerge from their cocoons). As they begin to move within the cocoon, workers notice the vibrations and assist the callow (new) workers to emerge. As callows eclose, the new eggs begin to hatch into larvae. An active larval brood stimulates the workers of the colony chemotactually, energizing the colony to a “high pitch” during the larval development, and the nomadic condition is begun and maintained. As the larvae of Eciton burchelli pass through five larval instars before pupating, nightly migrations of the bivouac are necessary in order to provide the high fat diet needed for the brood to develop. (Akre, 1968; Holldobler and Wilson, 1990; Schneirla, 1949; Schneirla, Brown, and Brown, 1954)

Workers live for several months while queens may live for several years. Little information is known about the exact lifetimes as this species is very difficult to keep in captivity, and its nomadic behavior makes individuals very difficult to track over long periods of time. (Gotwald, 1995)

Army ants (Dorylinae) are characterized by their unique nomadic behavior pattern and purely carnivorous diet (Schneirla 1956, Schneirla et al. 1954). Eciton burchelli and its close relative, Eciton hamatum are fully terrestrial (Schneirla, 1947), unlike many other army ant species even within the same genus (Schneirla et al 1954). Eciton burchelli are swarm raiders, foraging in a dense fan shaped swarms that can span several meters across, attached to the temporary nest (bivouac) by a single column that can itself extend over 200 meters. Their large colony size of 100,000 to 2,000,000 adult individuals (Gotwald, 1995) make their foraging swarms especially intimidating. The most distinguishing feature of army ant behavior is the two regularly alternating phases of colony life. During the nomadic phase there are major foraging raids each the day ending in a change of nest location, while the stationary colonies go out on less vigorous and less frequent foraging raids, with the nest site remaining constant (Schneirla 1947, and Schneirla et. al 1954). Bivouac structure is comprised of living workers clinging together by specialized tarsal hooks (Schneirla, 1956). (Gotwald, 1995; Holldobler and Wilson, 1990; Schneirla, 1947; Schneirla, 1956; Schneirla, Brown, and Brown, 1954)

Army ants, like all ants, have a variety of ways to communicate with one another. Most important are chemical signals. Chemicals called pheromones can be released into the air to signal alarm, food, or used for recognition of a nest mate. Workers also use chemicals to mark foraging trails by wiping their abdomens on the ground as they walk. Chemicals can additionally be used to communicate needs for assistance, food, tropholaxis (the exchange of oral or anal fluid), control of reproduction within the colony, and sexual communication. In addition to chemical signals, army ants communicate with vibrations and touch. Army ants do not rely on visual communication as they are almost completely blind. (Holldobler and Wilson, 1990)

Army ants work together to catch, subdue, and carry their prey back to the bivouac. They subdue prey with powerful stings, while also pulling off legs and antennae using mandibles made for pinching and gripping. Their sharp pointed mandibles do not have a good cutting edge, so anything too big to be carried back that cannot be easily pulled apart is left behind. Foraging direction during the stationary periods shifts 123 degrees per raid, while foraging during the nomadic phase tends to be in the same direction everyday. (Franks, 1982; Holldobler and Wilson, 1990; Schneirla, 1956)

Although insect types comprising the Eciton burchelli diet vary slightly between wet and dry seasons, it is consistently diverse and high in fat. Franks (1987) found that during the wet season the majority of food items brought back to the nest are wasp and ant broods, while cockroaches and crickets predominate in the dry season. Schneirla (1956) observed significantly more variation year round, with tarantulas, scorpions, beetles, roaches, grasshoppers, as well as other hymenopteran adults and broods, and other insects, making up their diet. He also witnessed snakes, lizards, and nestling birds being attacked, although there are no accounts of vertebrate prey being carried back to the bivouac. Other arthropods escape through excitatory secretions, repellent chemicals, or tonic immobility. (Franks, 1982; Holldobler and Wilson, 1990; Schneirla, 1956)

Many Eciton colonies have been observed to contain “ecitophiles”, beetles and other arthropods that rely on these ants (Schneirla 1956). Eciton burchelli is specifically known to have relationships with Euxenister beetles which live in the nest, travel with the bivouac, groom adult workers, and indiscriminately feed off booty and broods (Akre 1968). Several species of mite also call the army ant bivouac home, while thousands of small vertebrates and invertebrates alike are gobbled up by ant birds (including Formicariidae and Thamnophilidae) while escaping the attacking ant swarm. Ant birds are birds from at least four different families that depend heavily upon the swarming army ants to disturb small animals that are then gobbled up. These birds are commonly found following ant foraging trails. (Akre, 1968; Gotwald, 1995; Schneirla, 1956)

Although E. burchelli has a painful sting and will agressively protect the bivouac and fellow workers, this species does not frequently come into contact with people.

Eciton burchelli can be very beneficial in terms of removing agricultural and household insect pests. (Gotwald, 1995)

There is no special status for these ants.

'California Academy of Sciences http://www.calacademy.org' 'New World Army Ants http://www.armyants.org'