Weaver ants or green ants (genus Oecophylla) are eusocial insects of the family Formicidae (order Hymenoptera). Weaver ants live in trees (they are obligately arboreal) and are known for their unique nest building behaviour where workers construct nests by weaving together leaves using larval silk.[3] Colonies can be extremely large consisting of more than a hundred nests spanning numerous trees and containing more than half a million workers. Like many other ant species, weaver ants prey on small insects and supplement their diet with carbohydrate-rich honeydew excreted by small insects (Hemiptera). Weaver ant workers exhibit a clear bimodal size distribution, with almost no overlap between the size of the minor and major workers.[4][5] The major workers are approximately 8–10 mm (0.31–0.39 in) in length and the minors approximately half the length of the majors. Major workers forage, defend, maintain, and expand the colony whereas minor workers tend to stay within the nests where they care for the brood and 'milk' scale insects in or close to the nests.
Weaver ants vary in color from reddish to yellowish brown dependent on the species. Oecophylla smaragdina found in Australia often have bright green gasters. Weaver ants are highly territorial and workers aggressively defend their territories against intruders. Because they prey on insects harmful to their host trees, weaver ants are sometime used by indigenous farmers, particularly in southeast Asia, as natural biocontrol agents against agricultural pests. Although weaver ants lack a functional sting they can inflict painful bites and often spray formic acid[6][7] directly at the bite wound resulting in intense discomfort.
The weaver ants belong to the ant genus Oecophylla (subfamily Formicinae) which contains two closely related living species: O. longinoda and O. smaragdina.[1] They are provisionally placed in a tribe of their own, Oecophyllini. The weaver ant genus Oecophylla is relatively old, and 15 fossil species have been found from the Eocene to Miocene deposits.[2][8] Three other genera of weaving ants, Polyrhachis, Camponotus and Dendromyrmex,[9] also use larval silk in nest construction, but the construction and architecture of their nests are simpler than those of Oecophylla.[10]
The common features of the genus include an elongated first funicular segment, presence of propodeal lobes, helcium at midheight of abdominal segment 3 and gaster capable of reflexion over the mesosoma. Males have vestigial pretarsal claws.[11]
Oecophylla have 12-segmented antennae, a feature shared with some other ant genera. The mandibles each have 10 or more teeth, and the fourth tooth from the tip is longer than the third and fifth teeth. The palps are short, with the maxillary palps being 5-segmented and the labial palps being 4-segmented. The mesonotum is constricted and (in dorsal view) narrower than the pronotum and propodeum. The node of the petiole is low and rounded.[12]
O. longinoda is distributed in the Afrotropics and O. smaragdina from India and Sri Lanka in southern Asia, through southeastern Asia to northern Australia and Melanesia.[13] In Australia, Oecophylla smaragdina is found in the tropical coastal areas as far south as Broome in Western Australia and across the coastal tropics of the Northern Territory down to Yeppoon in Queensland.[14]