The Original Farmers: Leaf-Cutter Ants

Humans began farming around 12000 years ago, and while many think that this is a feature unique to humans, it is prevalent in a few other species of animals, including leaf-cutter ants, whose ancestors began farming 60 million years before humans.

(Leaf cutter ants carrying pieces of leaves back to their colony to feed their fungus farms which are their main source of food)

There are 240 species of attine ants, leaf cutters included among them, who are known to practice agriculture. These fungus-farming ants, all from the subgroup Attini, first appeared in the rainforests of South America. They originated as most other ant species that foraged for food. However, 60 million years ago, a mass extinction occurred called the Cretaceous-tertiary extinction that wiped out an estimated 75% of all of Earth’s species (including the dinosaurs). It is believed that this extinction is what caused the Attine ants to start farming fungus, since the lack of sunlight caused masses of plants to die off and the animals that relied on them, making it difficult to forage for food, but allowed many fungi to thrive because they are decomposers and could get their nutrients from dead bodies, making them a good food source.

During this period, some species of Attine ants practised a form of lower agriculture (and some still do), which is when the crops that the ants are cultivating are not completely domesticated and are not completely reliant on the ants to survive/they can survive in the wild. So if the fungus were to die out, the ants would be able to replace them with another wild variant. Then, a second agricultural revolution happened around 35 million years ago which caused some species of the ants to begin practising a form of higher agriculture, which is when the crops that are being farmed are completely reliant on their farmers and cannot survive or exist in the wild.

This second agricultural revolution occurred during the Eocene-Oligocene event, which was a period of global cooling. This cooling allowed drier biomes to expand. So, some species of Attine ants moved from wet rainforests to drier biomes, bringing the fungus with them, and growing them in controlled conditions that mimicked the wet rainforests where they came from. This then made the fungus reliant on the ants to grow, because they wouldn’t be able to survive in the outside environment. From a wet forest to a dry habitat along with being isolated for millions of years, the fungus eventually became domesticated by the ants, completely relying on them for survival, not being found in the wild at all. Not only do the fungus rely on the ants, but the ants also rely on the fungus. Early on in their evolution, leaf-cutter ants lost their ability to produce the amino acid arginine because it was available to them in the fungus, explaining why none of these species of ants have stopped farming since they started.

Leaf cutter ants cultivate monocultures (one crop) of this fungus. With human agriculture, cultivating monocultures comes with many issues like pests which arises the need for pesticides, which the pests can then build up a tolerance to, and diseases among many others. Leaf-cutter ants have developed a way around all of these issues. To deal with pests, they use their own form of pesticide that comes from bacteria that they grow in their nests and sometimes on their bodies. This also solves the issue of the pests building up a tolerance to the pesticides because by keeping live cultures of the bacteria, it can adapt to any tolerances that are built up. Leaf-cutter ants also prevent the spread of disease by keeping their underground farms extremely clean.

Leaf-cutter ants have extremely old and sophisticated methods of farming going back millions of years that humans have a lot to learn from, especially with their use of pesticides, and agriculture methods that allow them to farm while still retaining balance within their ecosystems.