Leafcutter ants create one of the most complex social societies on earth

Leafcutter ants are among the most fascinating creatures in the animal world. They form the most complex social structures, next to humans. Massive colonies may occupy almost a square kilometer and may contain as many as 8 million individuals.

Highly specialized, they have four castes in their colonies, with the caste position being determined by size and function. One of the workers is a harvester, cutting leaves and carrying them back to the underground tunnels in the nest. They don't actually eat the leaves. They use them to grow fungus underground that becomes their food. In that sense, they are farmers and gardeners. They tend to their gardens, removing waste from the plants and also from the other ants.

The workers are so sensitive that they can detect chemical changes in the fungus that tell the ants if a leaf is unsuitable for their farms. They carry fungus on their bodies and react to the chemicals emitted by the fungus to decide if a species of plant is toxic to the fungus. They will discard these leaves and refuse to gather more of the same species. And if the wrong type of fungus infects their gardens, the ants will remove those leaves, much like we would remove weeds from a vegetable patch.

The larger workers are vulnerable to phorid flies that lay eggs in the crevices in their heads. Smaller workers, known as minims will ride on the large ants' backs to ward off attacks by these parasitical flies.

All ant colonies require a queen. She hatches and flies from the nest in search of new ground and a new place to begin a colony. She leaves her nest, becomes impregnated and is soon ready to lay eggs. She also carries a small portion of seed fungus to begin a new farm and food source. The odds are against her as only 2.5 per cent of queens will manage to establish a successful colony.

Leafcutter ants have been harvesting and growing food like this for more than ten million years. Although an individual leafcutter ant will typically live for 6-10 weeks, their colonies may survive for thousands of years.