Ants are small creatures. Even the relatively large Weaver Ant is less than 1 cm in length. However, "small" does not necessarily mean "weak". Quite the contrary; in solidarity, ants are very powerful and can fight intruders many times bigger than them. The little ants are champions of cooperation and each contributes to the survival of the whole colony.
Weaver Ant (Oecophylla smaragdina) is the commonest ant in Hong Kong and is easily identified. For one, these ants are "large": the male is about 7 mm in length and the queen can grow up to 18 mm. They are also distinguished by the yellowish orange colour!
Weaver ants are fierce fighters. Once threatened, they will hold up their abdomen and open the mandibles wide as a warning signal. If the intruders do not retreat, the ants will launch attacks with biting and formic acid ejection from the tail. Their aggressive nature makes them ideal for biological control in orchards. Literature shows that as early as in the Tang Dynasty, citrus trees harbouring weaver ants were well protected from pest damage. Hence, weaver ant husbandry in citrus orchards was common practice.
Weaver ants live on trees. Apart from citrus trees, they inhabit other trees too. So you can hardly find them on the ground. Look up at a tree, and if you see a ball-shaped object made out of fresh leaves, it is very likely the nest of weaver ants.
Spirit of Cooperation
How can the small ants build a nest up in a tree? This is the work of not a single ant but a full team involving hundreds of worker ants and even the immature larvae. It is not easy work at all!
To construct a nest, numerous leaves must be pulled together. Yet the distance between the leaves is huge for the tiny ants. Therefore, the worker ants have to form an "ant chain" with their bodies. The frontline ants bite on the leaf margin with their mandibles, while the following ants hold tightly to the waists of the ants in front of them, forming an ant chain that eventually reaches another leaf. Then, all the ants pull the leaves together with all their force. Meanwhile, the larvae are carried to the joints, where silk is excreted to glue the leaves together. The procedure must to be repeated many times in order to complete a nest for the colony!
In defence, a weaver ant colony will send out its army. However, as opposed to sending the best soldiers to the frontline, the old and weak ants will take up the task for they are incapable of taking care of the larvae and carrying out other important tasks. They will sacrifice themselves to form the first defensive line for the colony. How amazing this is!