Parasol ants

Parasol ants are a striking example of insect agriculture in The Selfish Gene: they build immense underground colonies, cultivate fungi on prepared compost, and feed the resulting crop to themselves and their brood. Their farming shows how a species can reorganize its way of life around another organism, in a relationship that may benefit both partners.

Colonies and underground farms

Several New World ant species cultivate fungus gardens, and the practice evolved independently among African termites. Among the ants, Parasol ants are described as especially successful: single colonies containing more than two million individuals have been found. Their nests spread through underground passages and galleries reaching depths of ten feet or more, excavated from as much as forty tons of soil.

The fungus gardens occupy chambers within these extensive nests. Workers prepare special compost beds by chewing leaves into fragments and sowing a particular species of fungus in them. The colony’s appetite for leaves is therefore immense, and its leaf gathering can make Parasol ants a major economic pest. But the leaves are not directly eaten as food: they are the raw material from which the ants cultivate their crop.

Cultivation and mutual dependence

The ants eventually harvest the fungi, eat them, and feed them to their brood. The arrangement benefits the ants because the fungi break down leaf material more efficiently than the ants’ own stomachs do. The fungus may benefit as well: the ants propagate it more effectively than it could disperse its own spores, and they weed the gardens, removing alien fungi that would otherwise compete with the cultivated species.

This exchange is described as a possible form of mutual altruism: the ants provide cultivation and protection, while the fungus supplies food. The comparison with termites matters because it shows that fungus farming is not a single inherited arrangement, but one that evolved independently in unrelated groups. In both cases, a worker’s effort is directed toward a crop rather than toward gathering immediately edible food.

Place in the book’s evolutionary argument

The fungus gardens appear in a broader discussion of the ways organisms and their genes can benefit through relationships that cross the boundaries of individual bodies. The book distinguishes this kind of farming from the metaphor of a gene farm, in which workers use their mother as an efficient producer of copies of their genes. Parasol ants’ cultivation is instead literal agriculture: settled food production, discovered by social insects long before humans adopted it.

Their gardens make the book’s evolutionary reasoning concrete. The relationship can be cooperative without requiring either partner to act from foresight or generosity: the ants gain a more efficient food source, while the fungus may gain propagation and protection. The example thus presents cooperation not as a contradiction of evolutionary self-interest, but as an arrangement that can persist when its effects favor the participants.