Leafcutter ant

Leafcutter ants grow their own food.

They chew the leaves into soft mush. A fungus grows on it, like a fluffy garden. The ants and their babies eat the fungus.

The ants and their fungus need each other. Workers carry leaf pieces into the nest, where smaller ants cut them into tiny bits about 1 to 2 millimeters across. Gardener ants crush the bits, add droplets of their own droppings as fertilizer and press them into the spongy fungus garden.

The fungus grows little swollen tips full of food. Workers pick them and feed the juice to the young ants, which eat nothing else. Grown-up workers also sip sweet plant sap and nectar. The ants collect most of their leaves high up in the treetops.

Leaf fragments are the substrate for a specialized cultivated fungus, Leucoagaricus gongylophorus. An assembly line processes them: foragers drop fragments in the nest, processing ants clip them to about 1 to 2 millimeters, and gardeners crush them into pellets, add fecal fluid and insert them into the garden, seeding them with fungal strands.

The fungus produces gongylidia, swollen hyphal tips that grow in clusters called staphylae, rich in lipids and carbohydrates. Larvae depend entirely on them, and most of the energy needs of workers are met the same way, although adult foragers also take plant saps and nectar, and Shik and colleagues (2018) found foragers more nutritionally flexible than once thought. Harvest comes mainly from the tree canopy, along with flowers and fruit parts.

Leafcutter ants walk along smooth paths, like little roads.

Some tiny ants ride on top of the leaves. They chase away flies that bother the carriers.

Leafcutter ants build trails like highways, cleared of plants and kept tidy. Some are longer than 500 meters and are used for months or years. The ants follow scent trails that they lay down on the ground.

Watch a leaf piece closely and you may see a tiny ant riding on top. These hitchhikers are minims. They guard the carrier from small parasitic flies that try to lay eggs on the ants, and they start cleaning the leaf on the way home. Colonies can work in the daytime or at night, and they cut back their work during rainstorms.

A. cephalotes is often called a superorganism: a queen and her sterile daughters with overlapping generations and a size-based division of labor. Foragers travel cleared trunk trails, some more than 500 meters long, maintained for months or years and marked with trail pheromones; fallen logs and roots are built into the network, and walking on them is faster.

Minims riding on fragments defend against parasitic phorid flies and begin cleaning the leaves. Activity varies by colony: some are diurnal, some nocturnal, and daytime parasitism and rain likely suppress daytime foraging. Foragers can work at surface temperatures from 17 to 45 °C. Refuse workers are kept apart from the rest of the colony, which helps protect the garden from pathogens.

There are lots of leafcutter ants.

They help forests by moving soil and leaves. Sometimes they also cut leaves on farms, and the farmers are not happy!

Atta cephalotes is common and widespread, so it is not in danger. Scientists have not given it an IUCN conservation status. It actually becomes more common where people have cut gaps in forests for farms, pastures and roads.

Leafcutter ants change the forest around them. They move huge amounts of leaves and soil, so scientists call them ecosystem engineers. On farms and in gardens, though, leafcutter ants can strip crops, and they are treated as serious pests in some places.

A. cephalotes has not been assessed by the IUCN and is not listed by CITES; the San Diego Zoo Wildlife Alliance describes it as abundant and widespread, with no conservation concern. It lives at low densities in undisturbed forest but thrives in forest gaps, edges and fragments, pastures and other human-modified land.

Its nests reshape soil and plant communities, which is why it is called an ecosystem engineer, and AntWiki notes that its large nests affect the leaf-litter animal community around them. In agricultural and urban areas, Atta species are considered severe pests, and human movements and attempts to wipe them out with chemicals have also shaped A. cephalotes populations (Weber 1969; Muñoz-Valencia and colleagues 2022).