Weaver ant:

The tiny arboreal nest weaver

by W.M.C.D. Wijekoon

The Weaver ant is an elegant tiny insect, found in Indo-Malayan region and Middle African areas of the world. They depute the Genus-Oecophylla, one of the largest ant Family-Formicidae and commonly named as Weaver ant. The well-known "Dimiya" (Oecophylla smaragdina) is the species distributed in Asian and Australian region.

They are obligatory arboreal and are known for their unique nest building behaviour where workers construct nests by weaving together leaves using larval silk. First they find leaves that are soft and easy to bend. Then ants pull the two edges of the leaf together slowly.

More and more workers join and pull until the two edges are nearly touching. Next, other worker ants carry larvae from the old nest and gently squeeze them between their mandibles.

This causes the larvae to ooze a thin thread of silk. Such like nests might be in size between smaller to larger. Colonies can be extremely large consisting of more than a hundred nests spanning numerous trees and contain more than half a million workers. Research findings revealed that, the "Dimiya" more tend to build their nests in trees of Annona sp (Vel atha), Calotropis gigantean (Wara), Acacia spp, Elaeocarpus serratus (Veralu), Syzygium malaccensis (Jambu).

Indoor and outdoor habitats are also used for their nesting and milky white webs can be seen in such nests.

Activity

Another fascinating behaviour of Weavers or "Dimiya" ant is that they show territorial activity of inhabiting colony trees.

A recent study revealed that Anopholepis gracilipes / Ambalaya ant is one of the territorial ants and when Weavers come close to them, they tend to attack and ambush, although Weavers are larger ones and are very aggressive.

Thus, in the environment you can see these two species inhabit in colonies of separate trees.

A large number of members in their colony consume a significant amount of food, especially they feed on a variety of insects close to their nest such as other ants, fireflies, beetles, bugs and all kind of dead insects. As such, they play a significant ecological role in our environment, hunting and killing of potentially harmful plant pests.

Thus, they have traditionally been used as biological control agents in Asian countries. One of the experimental results in South East Asia has shown that, fruit trees harbouring Weaver ants produce higher quality fruits, showing less leaf damage by herbivoures and require fewer applications of synthetic pesticides.

However, that statement is debatable because other findings revealed that living of Weaver ants on fruit trees may create negative effects for the productivity.

Presence of ant colonies creates less performance by herbivores and therefore reduces seed dispersal by insects and other animals including pollinators.

In addition, Weaver ants have an indirect adverse effect on the productivity of trees by protecting sap feeding insects such as scale insects and leafhoppers from which they collect honeydew. Hence, by protecting these insects from predators they increase their population and increase the damage they cause to trees.

Some caterpillars of the Lycaenidae and Noctuidae butterfly families secrete honeydew that attracts these ants to protect and survival of them.

This is indeed an elegant scene of "Dimiya" ant, when they found a caterpillar of Centaur oak blue butterfly, then carry the caterpillar into Weaver's nest.

The scene has been studied by Douglas B. Ranasinghe, 2008, and is noted as a very common thing. Another interesting feature is that farmers in Vietnam and China also use Weaver ants as a form of weather forecasting, as a change in the insects' behaviour can denote an impending storm.

Inhabiting as a group is more significant for them for protection and they have a strong chemical in their body "formic acid" which can be used for their protection and protect the nest from predators. Although ants do not have a stinger, they can inflict a painful bite which is aggravated by irritating such chemical from their abdomen.

Significance of "Dimiya" ant gives ideas to promote the agricultural practices among our farmers.