The yellow crazy ant (Anoplolepis gracilipes) is a species of ant which is believed to have originated in West Africa. This non-native species is one of the biggest invasive ant species ranging between 1 and 2 cm in size. Also known as the long-legged ant, it is easily recognised by its long legs and extremely long antennal scapes, and distinct yellowish colour. Unlike Oecophylla smaragdina (also known as the weaver ant or kerengga, locally), A. gracilipes has a more compact petiole.
Known to be ready invaders of disturbed habitats such as urban areas, forest edges or agricultural fields, the yellow crazy ant is easily adapted to and becomes dominant in new habitats due to its traits, such as aggression towards other ant species, efficient recruitment, and large colony size. It is called "crazy" because of its erratic movements when disturbed, and the International Union for Conservation of Nature (IUCN) has listed this species as one of the "One Hundred of the World's Worst Invasive Species".
Anoplolepis gracilipes is a scavenging predator and has a broad diet. It consumes a wide variety of foods, including grains, seeds, arthropods, and decaying matter, including vertebrate corpses. This species has also been reported to attack and dismember invertebrates such as small isopods, myriapods, molluscs, arachnids, land crabs, earthworms and insects (O’Dowd, 1999). However, it gets much of its food requirements from scale insects which are serious plant pests that feed on the sap of trees and release honeydew, a sugary liquid. These ants feed on the honeydew, and in return protect the scales from their enemies and help spread them to other trees; an example of mutualism. The honeydew not consumed by the ants accumulates on the leaves and stems of the trees and encourages the growth of sooty mould which gives the plants an ugly black appearance.
In Malaysia, even though A. gracilipes has established colonies in urban areas and some disturbed forests, it has yet to invade our natural forest. This species can be easily found scavenging for food around us. When disturbed it moves erratically compared to the kerengga. However, kerengga inflict a painful bite due to the production of formic acid while the yellow crazy ant does not bite at all. Fortunately the extent of its damage in Malaysia is unlike that observed in northern Australia and Christmas Island where the ants have caused serious ecological damage and formed supercolonies, especially on Christmas Island (O’Dowd 2009). It is believed that this ant species has not been able to invade our natural forest because it prefers hot and exposed areas unlike the closed, wet and humid environment of our natural forest.
