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Eciton burchellii

By Sara Diamond

Geographic Range

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

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. (Akre, 1968; Franks, 1982; Holldobler and Wilson, 1990)

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. (Franks, 1982)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    3 to 12 mm
    0.12 to 0.47 in

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. (Akre, 1968; Holldobler and Wilson, 1990; Schneirla, 1949; Schneirla, et al., 1954)

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. (Holldobler and Wilson, 1990)

On the queens propodium and petiole are horns pointed behind her. Males have been observed to grasp these horns with their mandibles while mating. (Gotwald, 1995)

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. (Holldobler and Wilson, 1990)

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. (Akre, 1968; Gotwald, 1995; Schneirla, 1947)

  • Breeding interval
    The queen lays a new cycle of eggs aproximately every three weeks.
  • Breeding season
    Internally fertilized eggs are layed in three week cycles year round. Mating must take place only once (although it may happen up to five times) in the life of each queen.

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. (Gotwald, 1995)

  • 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. (Gotwald, 1995)

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). (Gotwald, 1995; Holldobler and Wilson, 1990; Schneirla, 1947; Schneirla, 1956; Schneirla, et al., 1954)

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. (Holldobler and Wilson, 1990)

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. (Franks, 1982; Holldobler and Wilson, 1990; Schneirla, 1956)

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. (Franks, 1982; Franks, 1982; Holldobler and Wilson, 1990; Schneirla, 1956)

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

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. (Akre, 1968; Gotwald, 1995; Schneirla, 1956)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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

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

Conservation Status

There is no special status for these ants.

Contributors

Sara Diamond (author), Animal Diversity Web.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

eusocial

the condition in which individuals in a group display each of the following three traits: cooperative care of young; some individuals in the group give up reproduction and specialize in care of young; overlap of at least two generations of life stages capable of contributing to colony labor

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polarized light

light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

year-round breeding

breeding takes place throughout the year

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. 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.

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.

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

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