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Oecophylla smaragdina (Family Formicidae)

Green Tree Ant

Distribution:

This species occurs throughout the South-east Asian region, and the higher rainfall areas of northern Australia, from Broome in Western Australia to Mackay in Queensland. (WA, NT, QLD)

Features:

Australian populations of Oecophylla smaragdina have a strikingly green gaster (hind section), whereas elsewhere in the world the ants are uniformly yellowish.

Ecology/Way of Life:

Green Tree Ants are a leaf-nesting species of forests and denser woodlands. They are general predators, scavengers and nectar feeders. Honeydew from sap-sucking insects is especially important to them, and some leafy nests appear to be built specifically as shelters for such insects.

Along with the very similar Weaver Ants, Oecophylla longinoda, from Africa, the Green Tree Ant is famous for the way it builds its leafy nests. Leaves are pulled together by chains of workers, and 'weaved' into place using silk from larvae. Such nest-building behaviour is frequently cited as a classic example of cooperation within social insects. Workers will often form chains to pull distant leaves together, with one worker seizing the next worker's waist with its mandibles. As the leaves are held in place by lines of workers, other workers manipulate larvae in their mandibles to bind the leaves together.

A single Green Tree Ant colony consists of multiple nests, often spread through several trees. A large colony can contain over 100,000 workers, housed in more than 100 nests. Despite such large numbers of dispersed nests, mature colonies appear to be controlled by a single queen. Interestingly, however, new colonies are founded by multiple queens acting cooperatively, a process known as pleometrosis. This process also occurs in some other ants, and has the general advantage of leading to a more rapid production of a foraging workforce. There is an additional factor for Green Tree Ants – nest-founding queens require workers and silk-producing larvae to build their nests, and until this occurs they remain exposed to the elements. The process by which a single queen ultimately prevails in a mature colony is not yet known.

Interaction with Humans/Threats:

Green Tree Ants can be particularly common in urban parks and gardens, probably because these are watered throughout the tropical dry season. As residents and visitors to far northern Australia know all too well, the ants defend their nests and territories aggressively. Such aggression can be used to good effect in tropical orchards to control unwanted pests. Indeed, ancient records suggest that Green Tree Ants were carefully managed to control citrus pests in southern China as long as 1700 years ago. This represents the earliest known case of biological control of insects in the history of agriculture.

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