Leaf-cutter ant (Atta cephalotes)
|Size||Queen length: 22 mm (2)|
Male length: 18 mm (2)
Worker length: 2 - 14 mm (2)
This species has yet to be classified by the IUCN.
Atta cephalotes is a leaf-cutting, fungus-growing ant, with one of the most fascinating and complex social systems known to science. Colonies of this leaf-cutter ant species contain millions of individuals, making it possibly the most dominant invertebrate in Central and South America (3) (4) (5). A colony is made up of different classes of ant, known as castes, including the queen, workers, and at certain times, males and females (queens) that are capable of reproduction. Each individual within the colony carries out a specific job depending on its size and caste, in a behaviour known as ‘task partitioning’. As in all ant species, individuals in the worker caste of the leaf-cutter ant are wingless, sterile females of different sizes, depending on the role played within the colony (6). ‘Soldiers’ act to protect the colony and are the largest in the worker caste. A nest of the leaf-cutter ant will also contain tiny ‘minima’ workers, which work inside the colony and in the fungus garden, and ‘media’ and ‘maxima’ workers, larger ants with powerful jaws, which cut and transport leaf fragments back to the nest. Males are bigger than the workers, whilst the queens are larger still. Within a colony, only the males and the new queens will develop wings (2) (7) and are able to mate.
Widely distributed throughout Central and South America, ranging from Mexico in the north to Argentina in the south (2) (4).
The leaf-cutter ant is highly specialised to live in forest gaps, and colonies are most often found on farms and plantations, in rainforests, and in forest patches (usually mature or old-growth forest) (2) (4) (8).
The leaf-cutter ant lives in huge underground nests, connected by a series of tunnels (2). The ants cultivate a special ‘fungus garden’ deep within the nest, and are almost entirely dependent on the fungus for food (2) (5) (9). Maintaining the garden is crucial to the survival of the colony, and worker ants perform a variety of tasks, including foraging for leaves, cutting them into suitably sized fragments, transporting leaf fragments back to the colony, and preparing a ‘mulch’ (made from the leaves), which is used to cultivate the fungus garden (2) (5). Some of the smaller ants ‘hitchhike’ on leaves carried back to the colony, and are thought to protect the foraging ants from parasitic flies (Phoridae), and may also play a part in leaf preparation (7). It is essential that the fungus garden remains free of parasites that could cause disease, which would be devastating to the leaf-cutter ant colony. Microorganisms that have the potential to be harmful to the fungus are removed by some of the smaller garden workers as waste, which is taken to a separate waste chamber, reducing the chance that the fungus, or other ants in the colony, will become infected by harmful pathogens (5) (10).
In a colony, only the queen is able to produce offspring. The queen is capable of laying thousands of eggs per day, most of which are destined to become workers, with only a small number of these developing into males and females capable of reproduction. At the beginning of the rainy season, fertile individuals leave the nest to take part in a ‘nuptial flight’, a single flight during which mating occurs, and after which the males die (2) (6) (11). This is the only time that the females mate, and the potential queens are capable of storing several hundred million sperm, which are used to fertilise the eggs in a future colony (11). A new colony is created by a solitary female queen, who will dig a tunnel, and, using a tiny piece of fungus brought from the old nest inside a special cavity in the mouth, will start to cultivate a new fungus garden and begin egg laying (2) (8) (11) (13). Despite the large numbers of leaf-cutter ant queens that attempt to establish a colony, very few actually survive, with the probability that the founding queen will die before eggs hatch and the fungus garden becomes established estimated at nearly 90 percent (2).
The leaf-cutter ant is perceived as a major pest species because of the damage it can cause to agricultural ecosystems. The ant is able to defoliate (remove the leaves from) a wide range of plant species, including crops, and estimates made by scientists studying the ant suggest that within the territory of an Atta cephalotes colony, between 13 and 20 percent of new plant growth each year is cut and removed (2) (4) (9) (12).
There is some indication that in parts of its range, populations of the leaf-cutter ant may have declined due to increasing changes in land-use and forest fragmentation (4). Although the leaf-cutter ant is adapted to living in forests gaps, and has been known to use land that has been cleared for human use (8), it is likely that extensive fragmentation will lead to declining habitat suitability, and perhaps localised extinctions of some populations of this particular species of leaf-cutter ant (4).
Although regarded as a pest, the leaf-cutter ant is vital to maintaining the balance of the ecosystem in South and Central America, having evolved as part of the natural environment there for millions of years (8) (13). The ant plays an important role in trimming vegetation, stimulating new plant growth each year, breaking down plant materials and adding nutrients to the soil (2) (8). There are currently no conservation measures in place to protect the leaf-cutter ant, partly due to its status as one of the most dominant invertebrates of the region, and partly because of its role as a serious crop pest. Nevertheless, Atta cephalotes remains one of the most intensively studied insect species in the Americas, if not worldwide.
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- Caste: in social insect colonies, a group of individuals that are structurally and/ or behaviourally distinct, performing certain tasks. Examples are the soldier caste of termites and ants, and the workers of bees.
- Colony: a group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids or ‘individuals’), which are produced by budding and remain physiologically connected.
- Fertilise: the fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
- Invertebrates: animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones), echinoderms, and others.
- Parasite: an organism that derives its food from, and lives in or on, another living organism at the host’s expense.
- Parasitic: describes an organism that derives its food from, and lives in or on, another living organism at the host’s expense.
- Pathogen: any organism or substance with the ability to cause disease.
- Symbiotic: describes a relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
ITIS (July, 2010)
CariPestNet (July, 2010)
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- Correa, M.M., Bieber, AG.D., Wirth, R. and Leal, I.R. (2005) Occurrence of Atta cephalotes (L.) (Hymenoptera: Formicidae) in Alagoas, northeastern Brazil. Neotropical Entomology, 34(4): 695-698.
- Hart, A.G., Anderson, C. and Ratnieks, F.L.W. (2002) Task partitioning in leafcutting ants. Acta Ethologica, 5: 1-11.
- Burnie, D. (2001) Animal. Dorling Kindersley, London.
- Linksvaye, T.A., McCall, A.C., Jensen, R.M., Marshall, C.M., Miner, J.W. and McKone, M.J. (2002) The function of hitchhiking behaviour in the leaf-cutting ant Atta cephalotes. Biotropica, 34(1): 93-100.
- Hölldobler, B. and Wilson, E.O. (1990) The Ants. Harvard University Press, Cambridge, Massachusetts.
Bristol Zoo Gardens (July, 2010)
- Hart, A.G. and Ratnieks, F.L.W. (2001) Task partitioning, division of labour and nest compartmentalisation collectively isolate hazardous waste in the leafcutting ant Atta cephalotes. Behavioural Ecology and Sociobiology, 49: 387-392.
- Baer, B. and Boomsma, J.J. (2006) Mating biology of the leaf-cutting ants Atta colombica and Atta cephalotes. Journal of Morphology, 267: 1165-1171.
- Cherrett, J.M. (1968) The foraging behaviour of Atta cephalotes L. (Hymenoptera, Formicidae). Journal of Animal Ecology, 37(2): 387-403.
- Mueller, U.G., Rehner, S.A. and Schultz, T.R. (1998) The evolution of agriculture in ants. Science, 281: 2034-2038.