This is a relatively large, yellow / orange ant that is about 4 - 5 mm in length. The abdomen is usually a uniform light yellow but sometimes has dark brown markings. Their legs and antennae appear very long in comparison with the body. They do not have a sting but can spray formic acid, which they use to subdue prey and act as a defence mechanism. The attractively coloured queens are much larger than the workers, averaging about 10 mm in length. The name ‘Crazy Ant’ arises from its characteristic behaviour, which is to run erratically in rapid movements when disturbed.
This species original natural habitat is not known, but it has been speculated that it originated in Africa, since the genus Anoplolepis is known to be almost exclusively African.
Because the ants will create nests in many different places, the most significant dispersal method these days is the human-mediated dispersal, where colonies are inadvertently transported to new locations by humans, in potted plants, containers, or rubbish. They are able to disperse via trucks, boats, and other forms of human transport. Because of this, it has been introduced into a wide range of tropical and subtropical environments where it has naturalized and spread. However, an interesting aspect of A. gracilipes historic distribution is when the world’s ant fauna was still very poorly known, the earliest ant surveys circa 1895 found it already widespread over southeast Asia and the islands of the tropical Pacific and the Indian Ocean. This makes one wonder how it had spread so far in those early days.
Anoplolepis gracilipes is primarily a species of the lowland, tropical rainforest, preferring moist forests or other humid habitats, and it is capable of establishing colonies in both disturbed and undisturbed habitats. They are a very opportunistic species and will nest underwood and stones, in other animals abandoned burrows, under dead bark on trees, in crevices between bricks, and even just under dead leaves lying on the ground. Hence in captivity, they seem to be quite happy in almost any type of artificial nest.
This species has been described as a ‘scavenging predator’ and has a broad diet, a characteristic of many successful invasive species. It consumes a wide variety of foods, including grains, seeds, arthropods, and decaying matter, including vertebrate corpses. They will also attack and dismember slow-moving invertebrates such as small isopods, arachnids, earthworms, and insects. The workers subdue their prey by holding it down and the workers then pull the prey’s appendages in different directions which pins them down, while spraying them with formic acid.
Like all ants, they require a protein-rich food source for the queen to lay eggs and carbohydrates as energy for the workers. They get their carbohydrates from plant nectar and honeydew-producing insects, especially scale insects and aphids. These are plant pests that feed on the sap of trees and release honeydew, a sugary liquid. Ants eat the honeydew and feed it to their larvae, and in return protect the scale from their enemies and spread them among trees, an example of mutual cooperation. A factor that may promote the success of invasive ants is their ability to exploit these carbohydrate resources. It has been hypothesized that these carbohydrate-rich resources promote ant invasions by providing high-energy fuel for greater activity, growth, and the establishment of dominant supercolonies.
The foraging activity of this species is controlled by their response to environmental factors notably temperature and humidity. The ants prefer to forage in high humidity and moderate temperatures. When the humidity falls and the temperature rises significantly, they will cease foraging. In the tropics, they forage more intensively at night and early morning. During the middle of the day when it is very hot and the humidity is low, they return to their nest.
Alates can be present year-round, but in most instances, initiation of the main alate brood follows the beginning of the wet season. This is also when available food becomes more frequently available and easier to find. Newly mated queens will frequently re-enter their original nest boosting the potential for population growth and when conditions are favourable, they will very quickly form vast supercolonies.
This species naturally spreads and colonizes new areas through ‘budding’ - when mated queens and workers leave the mother nest to establish a new one. Generally, colonies that disperse this way have a lower rate of dispersal, however, in this species, the newly mated queens are also capable of independent colony foundation. Alate queens can fly, and queens and males have been collected by light traps. If queens are isolated, they are capable of raising a brood on their own. Hence this species is capable of both independent and dependent colony foundation.
This is a species that easily becomes established and dominant in new habitat due to traits such as its aggression toward other ant species, especially when defending resources, efficient fast recruitment, ability to utilize a wide range of food sources, and large colony size. In a normal ant population, there is one queen with all of her adept followers. These colonies almost always fight with their neighbours, and in doing so, they keep each other under control. Rather than establishing several competitive nests with individual queens (as the majority of other ant species do), yellow crazy ants establish super colonies consisting of large interconnected nests containing multiple queens. By cooperating, they can successfully outnumber and displace other species, thereby dominating food and nesting resources.
When involved in a battle with another ant species, A. gracilipes will curve its abdomen up toward the head of its attacker and spray a defensive substance from poison glands located in the abdomen. This secretion is highly toxic to other ants and is a very effective defence. What these ants do to dominate a new habitat is to create interlinked super colonies; these can contain more than 1000 queens and hundreds of thousands of workers. When colonizing new habitats, the colony will spread out and establish new subcolonies in any available conducive space. In Seychelles, it has been recorded that established colonies of A. gracilipes will increase their range by as much as 400 m a year. Another survey on Christmas Island yielded an average spreading speed of three meters a day, the equivalent of one kilometre a year.
They are very adaptable to temperature and humidity and at an optimum temp of around 26°C the newly laid eggs will hatch into larvae after 12 – 15 days, and the larvae will mature and pupate after only 7 - 10 days. The new workers emerge from the pupae after another 11 - 15 days, giving a complete brood maturity cycle of between 30 - 40 days.
Summary: They are a good-sized attractively coloured ant, easy to keep and will adapt to most types of artificial nests. They can have multiple queens in a colony, will take a wide range of food and breed quickly. Recommended for beginners to exotics.