Eciton burchellii

Geographic Range

Eciton burchellii is found in the tropical regions of Central and South America.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Eciton burchellii 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.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest
• scrub forest scrub forest

• Other Habitat Features
• agricultural agricultural

Physical Description

Eciton burchellii 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.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry
• polymorphic polymorphic
• venomous venomous

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

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 burchellii 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.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

The queen is able to store sperm in order to fertilize all of her eggs after mating only once. It has been suggested that queens of this species may mate up to five times over their lifetimes, although more research is needed in this area. Eciton queens are unusual in that they do not have wings. A queen will mate when a winged male is discovered by foraging workers and brought back to the bivouac. A male army ant will only mate with one queen in his lifetime. After a short period, usually less than 48 hours, he will die.

On the queens propodium and petiole are horns pointed behind her. Males have been observed to grasp these horns with their mandibles while mating.

• Mating System
• polyandrous polyandrous
• eusocial eusocial

The stationary condition occurs when the larvae begin to pupate and the physogastric (swollen with eggs) queen lays eggs. Nomadic nights begin again when callow (new) workers emerge from the pupae and many thousands of eggs hatch into a new generation of larvae.

New colonies are formed when new queens emerge from their cocoons. Since army ant queens are wingless, workers bond to the queen through chemical scents as they care for her while still in the parent colony. Eventually, the group of workers that has bonded with the new queen will leave the parent colony and begin a satelite colony with their young, new queen. For the first several days workers often go back and forth between the satelite and parent colonies. After this new (virgin) queen has mated and the new colony begins to increase in numbers, it becomes its own full fledged colony, and workers from each colony no longer recognize each other and will fight members of the other as if they had never been related.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing
• delayed fertilization delayed fertilization

Ants provide for their developing brood with care. Although the queens only job is to lay eggs, the workers care diligently for every egg, larva, and pupa. Primary caretakers of broods are called minims, and tend to be smaller sized ants. As temperature and humidity change throughout the day, minims will move broods around within the colony so that abiotic conditions are always as favorable as possible for development within the colony. In addition to moving broods around within the bivouac, the bivouac itself changes shape in response to changing abiotic factors outside in order to keep conditions constant within the colony walls.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

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.

Behavior

Army ants ( Dorylinae ) are characterized by their unique nomadic behavior pattern and purely carnivorous diet (Schneirla 1956, Schneirla et al. 1954). Eciton burchellii 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 burchellii 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).

• Key Behaviors
• arboreal arboreal
• terricolous
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• nomadic nomadic
• social social
• colonial colonial

Communication and Perception

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.

• Communication Channels
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• scent marks scent marks
• vibrations vibrations

• Perception Channels
• polarized light polarized light
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

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.

Although insect types comprising the Eciton burchellii 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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• eggs
• body fluids
• insects
• terrestrial non-insect arthropods

• Foraging Behavior
• stores or caches food stores or caches food

Ecosystem Roles

Many Eciton colonies have been observed to contain “ecitophiles”, beetles and other arthropods that rely on these ants (Schneirla 1956). Eciton burchellii 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.

Economic Importance for Humans: Positive

Eciton burchellii can be very beneficial in terms of removing agricultural and household insect pests.

Economic Importance for Humans: Negative

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

• Negative Impacts
• injures humans
  • bites or stings
  • venomous venomous

Conservation Status

There is no special status for these ants.

Additional Links

Encyclopedia of Life

Contributors

Sara Diamond (author), Animal Diversity Web.

References

Akre, D. 1968. The Behavior of Euxenister and Pulvinister Histerid Beetles Associated with Army Ants. PanPacific Entomologist , 44: 87-101.

Brown, T. 2004. "Infinite World" (On-line). Accessed February 09, 2005 at http://www.infiniteworld.org/research/research%20background.htm .

Franks, N. 1982. Ecology and Population Regulation in the Army Ant Eciton burchellii . Pp. 389-403 in The Ecology of a Tropical Forest . United States of America: The Smithsonian Institute.

Gotwald, W. 1995. Army Ants: The Biology of Social Predation . Ithica, NY, USA: Cornell University Press.

Holldobler, B., E. Wilson. 1990. The Ants . United States of America: Harvard University Press.

Schneirla, T., R. Brown, F. Brown. 1954. The Bivouac or Temporary Nest as an Adaptive Factor in Vertain Terrestrial Species of Army Ants. Ecological Monographs , 24: 269-296.

Schneirla, T. 1947. A Study of Army-Ant Life and Behavior Under Dry-Season Conditions with Special Reference to Reproductive Functions.. American Museum Novitates , 1336.

Schneirla, T. 1949. Problems in the Environmental Adaptation of Some New-World Species of Doryline Ants.. Anales del Instituto de Biologia. , Tomo XX, Nos. 1 & 2.

Schneirla, T. 1956. The Army Ants. The Smithsonian Report, Report for 1955: 379-406.

Snelling, G., R. Snelling. 2002. "New World Army Ants" (On-line). Accessed February 09, 2005 at http://www.armyants.org .