Oecophylla smaragdina, commonly called the green tree ant or weaver ant, is a northern species that also occurs throughout South-east Asia and westward to India.  They can be conspicuous in forested areas within their range, foraging on vegetation as well as the ground, often in large numbers and forming distinct trails.  They are aggressive and highly visual and while they don't sting, they will inflict a painful bite followed by a squirt of formic acid from the tip of their gaster – a very effective deterrent for those invading their territory.

One of the most distinctive features of this ant is the way it constricts its nest, and is the reason for the common name 'weaver ant.'  They create nests by pulling living tree or shrub leaves together and stitching them with silk produced by special glands found in their larvae (adult ants do not produce silk).  Workers form living chains to pull and hold leaves in position, ready to be added to the nest.  Once in position other ants bring larvae to the construction site, gently squeezing them to encourage silk production, the silk being used to form a mess to tie leaves together and to fill small gaps between leaves.  The result is a secure and solid nest containing from a few to many dozens of leaves, all firmly held together and forming a well camouflaged shelter safe from predators and the elements.  As colonies grow, existing nests will be expanded and new, satellite nests added nearby.  Over time single colonies can grow to contain as many as 150 individual nests found in 30 or more adjacent trees.  Most colonies will contain more than one queen with all queens found together in a single nest.

Green Tree Ants are very aggressive foragers and will prey on essentially any small animals they come across.  They generally forage in groups and often take items much larger than themselves.  They are also particularly attracted to the sugar and protein rich secretions from extrafloral nectaries found on many plants and produced by insects such as some Homoptera and caterpillars.  These plants and insects take advantage of the highly predacious nature of these ants to protect them from attack by herbivores and predators.  Even humans have exploited this behaviour by moving ant nests into orchards where they will attack crop pests.  In China, as early as in 300 AD, nests were placed in citrus orchards and bamboo strips placed among the trees to encourage the ants to colonise all trees.  In this way the crop was protected from insect pests that would otherwise damage the fruit.  While more recent societies have investigated similar practices it has yet to be adopted to any significant extent.

However, it's not always clear that having these ants around is a benefit.  In some cases Green Tree Ants are known to discourage pollinators from visiting flowers on the trees they inhabit, reducing pollination levels and therefore seed production or fruit set.  This would disadvantage plants with ants compared to those without.

Some insects take advantage of these ants' sweet tooth for their own benefit.  For example the caterpillars of some butterflies, especially those in the families Lycaenidae and Noctuidae, secrete honeydew that attracts these ants.  The ants then spend considerable time tending the caterpillars, 'milking' them for honeydew by stroking them gently with their antennae.  In return, the caterpillars gain protection as the ants attack the predators and parasites that would otherwise attack them.  In some cases these caterpillars get an additional advantage by gaining entry into the ant's nest where they feed on the ants' larvae!  While a definite benefit for the caterpillars it's not so good for the ants.

Caterpillars aren't the only animals to take advantage of these ants.  Some jumping spiders mimic Oecophylla workers in both looking like them and, more importantly, by smelling like them with chemical mimicry.  Thus disguised, the spiders enter the ant's nest to devour both adult workers and larvae.  

Humans also find these ants tasty.  In markets in Thailand and the Philippines they are sometimes sold as food.  The taste of the pupae has been described as creamy while the adults are said to have as lemony or creamy and sour taste.  The Dayaks in Borneo are known to mix adult ants with rice for flavouring.  Fortunately for the ants this feeding behaviour appears to be restricted to only a limited number of human populations and a few adventurous souls from other regions.

This is only a brief summary of the extensive information available for this species.  For further details the extensive published and online literature concerning it should be consulted.