In Fiji, ants have learned to grow plants to house their massive colonies

A tree full of Squamellaria plants in Fiji. Each one has been carefully grown by ants, who live inside the plants' fleshy interior. It's like James and the Giant Peach, except not giant.

High in the trees on the Fiji islands, ants in the species Philidris nagasau are doing something extraordinary. They've brought in seeds from several species of a large, lumpy fruit from a plant known as Squamellaria and carefully planted them in the nooks and crannies of the tree bark. Once the plant takes root in the tree and begins to grow, the ants climb inside its young stalks and fertilize it. But then the real action starts. As the fruit swells, the ants move inside, carving tunnels and rooms into the fleshy interior. When the colony expands, it may include dozens of these fruits, which look like strange tumors sprouting from tree branches.

Though researchers have known for a while that ant colonies can live inside fruits, a new study in Nature Plants reveals that this housing arrangement is far more complex and ancient than we knew. University of Munich biologists Guillaume Chomicki and Susanne S. Renner went to Fiji to observe the ants and found that they inhabited six different species of Squamellaria. Each of these species evolved to grow in tree bark using a specialized root system called a foot. When the plants are still young, the ants enter a small cavity in the stalk called a domatium to fertilize it. Though the researchers never directly observed how the ants did the fertilizing, they speculate that basically the ants are pooping in there.

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