3 - Plant protection by direct interaction

Summary

Ants foraging on plants take a great variety of prey items including insects and other invertebrates that are either herbivores or seed predators. Therefore, the mere presence of hunting foragers can provide some defense against plant enemies. With few exceptions plants are hospitable foraging areas, and once ants have gained access, they will hunt and remove prey irrespective of the size, architecture, or morphology of the plant. Ants remove a great variety of animals that do damage even, as in the case of Monomorium floricola, entering the tunnels of leaf-mining beetles to kill the tiny occupants (Taylor 1937).

The protective character of ants foraging on plants has been recognized for hundreds of years. In various parts of China nests of the weaver ant Oecophylla smaragdina were taken from the forest around citrus and litchi groves and placed on branches of orchard trees. Branches close to the nest were smeared with wax to prevent the ants from leaving the trees, and until they established their food-gathering territory their diet was augmented with dog intestines or silkworm larvae. After several weeks the ants established territories and patrolled the trees aggressively for food. Bamboo poles were used to create bridges from trees with nests to those without, and the groves were soon a mosaic of Oecophylla territories. As long ago as the eleventh century A.D., the Chinese observed the ants removing a considerable variety of insect herbivores and seed predators in large numbers, including stinkbugs of the hemipteran family Pentatomidae, many of which feed on plant sap, and the larvae of the butterfly Papilio demoleus, which were killed by workers stretching the unfortunate victim in several different directions simultaneously and holding it in that position until it died.