There are 47 species of these leaf-chewing ants. These tropical, fungus growing ants are all endemic to South America and Central America, Mexico and parts of the southern United States. They cut and process fresh vegetation (leaves, flowers and grasses) to serve as the nutritional content for their fungal cultivation. They are almost entirely dependent on the fungus for food. They are also known as ‘parasol’ ants because of the way they carry leaves above their heads. They are capable of carrying over 50 times their own body weight. It also plays an important role in trimming vegetation, stimulating new plant growth each year and adding nutrients to the soil. A colony is made up of different classes of ant, known as castes including the queen, workers and at certain times males and females that are capable of reproduction.
Leaf-cutter ants practice advanced methods of sustainable agriculture, and operate one of the most studied social caste systems in the natural world. They consume more vegetation than any other animal group. Their own fungal secretion which they inject into the leaves, can change poisonous plants into a nutritious meal. The central mound of their underground nests can grow to more than 30 metres across. An average nest contains over 5 million ants. They secrete a chemical trail so they can always find their way back to the nest. They can travel several hundred metres in search of the right kind of leaves. They collect from all layers of the forest, from the floor to the upper canopy. If a particular type of leaf is toxic to the fungus, the colony will stop collecting it.
Colonies of this species contain millions of individuals, making it possibly the most dominant invertebrate in Central and South America. Each individual within the colony carries out a specific job depending on its size and caste. Soldiers act to protect the colony and are the largest in the worker caste. A nest of the leaf-cutter ant will also contain tiny ‘minima’ workers, which work inside the colony and in the fungus garden and media and maxima workers, larger ants with powerful jaws, which cut and transport leaf fragments back to the nest. Males are bigger (18 mm)than the workers, whilst the queens are larger still (22 mm). When the ants are out collecting leaves, they are at risk of attack by some species of phorid fly, that lay eggs into the crevices of the worker ants’ heads. Often a smaller ant will ‘hitchhike’ on leaves carried back to the colony and are thought to protect the foraging ants from parasitic flies.
Within a colony only the males and the new queens will develop wings and are able to mate. At the beginning of the rainy season, fertile females leave the nest to take part in a ‘nuptial flight’, a single flight during which mating occurs, and after which the males die.
Once on the ground, the female loses her wings and searches for a suitable underground lair in which to found her colony. The success rate of these young queens is very low, and only 2.5% will go on to establish a long-lived colony. To start her own fungus garden, the queen stores bits of the parental fungus garden in her pocket, which is located within her oral cavity. Each queen leafcutter ant can lay up to 30,000 eggs each day. If the queen ant dies, all the other ants die too. She lives at the heart of the colony.
Leafcutter ants can be a serious agricultural pest, defoliating crops and damaging roads and farmland with their nest-making activities. For example some species are capable of defoliating an entire citrus tree in less than 24 hours. The main predator of the leafcutter ants is the armadillo. However, as leafcutter ants are an integral part of the rainforest ecosystem, when the forests disappear, so do they.
Lloyd Boutcher,
Director, Sunvil Traveller
