Why do ants work in colonies?

Answer: Division of labor increases success

Learning from older ants — Learning does happen in ant colonies: some species teach nestmates the way to food by tandem running, one ant leading another and waiting for it to catch up, and foragers memorize landmarks. But that learning takes place inside a colony; it is not the reason colonies exist. Most of the colony's organization is instinctive, and its advantage is division of labor.

Ants enjoy social interaction — Ants have no sense of enjoyment to speak of, and a colony is not a social club. Each ant follows simple rules cued by smell and touch, and colonies persist because that arrangement raises the survival of the queen's offspring.

Division of labor increases success ✓ — Correct! An ant colony is a eusocial society: the queen lays the eggs, workers forage, build and nurse, and in many species larger soldiers defend. Some species go further and farm fungus or herd aphids. Pheromones coordinate all this without any leader. Because workers are close relatives of the queen's offspring, helping the colony spreads their own genes, and a colony of specialists out-collects and out-defends any insect living alone.