Leafcutter Ants (ARCtv S01 Ep 08)

Leaf-cutter ant societies are based on ant–fungus mutualism, a symbiosis between ant and fungal species. The ants actively cultivate fungus much like humans farm crops as a food source. The ants and fungi are dependent on each other for survival. They grow this fungus by creating gardens with leaf mulch, which is why they can be seen in their thousands carrying leaves through the forest to their nests. The ants have evolved to change food plants constantly, preventing a colony from completely stripping off leaves and thereby killing trees, thus avoiding negative biological feedback on account of their sheer numbers. However, this does not diminish the huge quantities of foliage they harvest. Once foraging workers locate a resource in their environment, they lay down a pheromone trail as they return to the colony. Other workers then follow the pheromone trail to the resource. As more workers return to the nest, laying down pheremones, the stronger the trail becomes. The strength to which workers adhere to the trail depends mostly on environmental factors, such as the quality of the resource. Colonies can contain more than 8 million ants, mostly sterile female workers.