“Even the sharpest ear cannot hear an ant singing” -Sudanese Proverb

(Red ant on Fijian palm leaf)

Just when you thought you’d heard it all, this week comes the revelation that a certain species of Fijiian ants has been growing plants for millennia.  And they’ve been doing so for far longer than humans. The ants have been growing crops and establishing their colonies within them all while tending their own teeny tiny community gardens.

Researchers from the University of Munich in Germany made the surprising discovery while studying a species of ants called Philidris nagasau. The ants, which are indigenous to Fiji, establish their colonies high in trees on the tropical islands. While observing the ants’ behavior, the scientists discovered that the insects had formed specialized communities devoted entirely to gardening. And they were growing fruit.

Tropical forest in Fiji

While the earliest known human farming dates back roughly 23,000 years, DNA evidence suggests that Philidris nagasau may have been growing plants as far back as 3 million years. And not only have they been growing fruit, they’ve been cultivating six different species of the same plant known as squamellaria. Squamellaria is a genus of flowering plants in the Rubiaceae family (that includes the coffee plant among others.) It is endemic to the islands of Fiji.

Squamelleria fruit in macaranga tree

Although many epiphytic plants (plants that grow harmlessly on other plants) have teamed up with ants before to gain nutrients, this is the first instance of a single species of ants actively engaged in planting and fertilizing the seeds of a plant.

How they garden

“The ant’s a centaur in his dragon world.” – Ezra Pound

It turns out that the Fijiian ants are involved in every aspect of gardening, from planting to harvesting, which has a direct impact on their housing and social behavior. The process begins even before the squamelleria are ripe, when the ants start gathering the fruits’ seeds and sowing them in elbows and cracks of the host tree’s branches. As the seeds germinate, the ants stand guard over the tiny sprouts, while fertilizing them with their feces.

Once the squamelleria begin to mature, they swell into soft, bulbous structures composed of many chambers called domatia. The domatia serve as the ants’ home once they’re large enough for the mini gardeners to enter. As the fruits expand in size, the chambers do, too, and more and more fertilizer-producing ants move in, thus establishing a relationship that is beneficial to both parties.

The ants live inside the domatium during the life of the squamelleria where they form ever expanding colonies. Once the fruit appears, the ants eat the sugary flesh, collect the seeds and repeat the cycle.

According to the researchers, each ant colony farms dozens of fruit plants at the same time, while producing a system of mini highways that link one to another. The entire connected network of community ant farms often encompasses many trees.

Researchers have never encountered these ants living anywhere other than in these fruits nor the plants living without the ants. Neither species can survive without the other.

The study was led by Professor Susanne Renner and Guillaume Chomick and published in the journal Nature Plants.