HUMANS began planting crops about 10,000 years ago. Ants have been at it rather longer. Leafcutters, the best known myrmicine agriculturalists, belong to a line of insects that has been running fungus farms based on chopped-up vegetable matter for 50m years. By that yardstick even Philidris nagasau, a species of Fijian ant, is a newcomer to farming. It started cultivating plants only about 3m years ago. What distinguishes it is that it is growing not only food, but also homes. It was already known that P. nagasau lives in epiphytes (plants that grows upon other plants) called Squamellaria. But as Guillaume Chomicki and Susanne Renner of the University of Munich describe in this week’s Nature Plants, it also sows and nurtures them.

Dr Chomicki and Dr Renner discovered, in the course of study of the six species of Fijian Squamellaria, that P. nagasau worker ants harvest seeds from their epiphytic homes, carry them away, and then insert them into cracks in the bark of suitable trees. That done, they patrol the sites of the plantings to keep away herbivores, and also fertilise the seedlings as they grow by defecating into hollow structures called domatia that develop in the bases of the plants’ stems.

As a Squamellaria grows, its domatium swells (see picture) and develops galleries that can accommodate ants—which then move in. This, and the plant’s habit of growing flowers that generate nectar long after they have been pollinated, provide the evolutionary quid pro quo that makes the relationship between insect and epiphyte work. Indeed, it works so well that P. nagasau has lost the ability to build its own nests. Its colonies sprawl over several Squamellaria plants, and grow by increasing the number of domatia they control.

Some other ant species sow seeds in order to glean nourishment from the resulting plant. Likewise, around 700 types of plants have domatia that house ants, which then protect their hosts from herbivores. But, as far as is known, none relies on those ants to scatter its seeds. Only in P. nagasau and Squamellaria has the symbiosis developed so far that neither plant nor ant can survive without the other.