To picture this farm, imagine some dark blobs dangling high up in a tree.
Each blob can reach “about soccer ball size,” says evolutionary biologist Guillaume Chomicki of Durham University in England. From this bulbous base, a Squamellaria plant eventually sprouts leafy shoots and hangs, slumping sideways or upside down, from its host tree’s branches. In Fiji, one of the local names for the plant translates as “testicle of the trees.”
Some Squamellaria species grow in clusters and teem with fiercely protective ants. As a young seedling blob plumps up, jelly bean–shaped bubbles form inside, reachable only through ant-sized doorways. As soon as a young plant cracks open its first door to daylight, “ant workers start to enter and defecate inside the seedling to fertilize it,” Chomicki says.
The idea that ants tend these plants as farmers gave Chomicki one of those surprise-left-turn moments in science. In a string of papers published since 2016, he and colleagues share evidence for the idea that the Philidris nagasau ants may be the first known animals other than humans to farm plants. (The other known insect farmers cultivate fungi.) Chomicki’s latest paper, in the Feb. 4 Proceedings of the National Academy of Sciences, reports that ants planting seeds of their blobby crop make trade-offs, going for full sun and maximizing the rewarding, sweet flowers rather than planting in the shade, where plants would have higher nitrogen.
Until Chomicki’s work, biologists accepted only three groups of fungus-farming insects as achieving the essentials of full agriculture and so rivaling human efforts. Select types of beetles, termites and ants each tamed different fungi, tending their much-needed food crop from sowing to harvest.
Humans didn’t farm any food before roughly 12,000 years ago as far as we know. Insects started much earlier. Even leaf-cutter ants, relative newcomers to farming, have been growing their specialized crops for about 15 million years.
To compare agriculture in insects and humans, entomologists, archaeologists and other specialists have held three gatherings in the last six years searching for principles and perhaps some practical advice. (A press fellowship from the Konrad Lorenz Institute for Evolution and Cognition Research paid for me to attend the 2019 symposium in Klosterneuburg, Austria.)
The fungus farms of leaf-cutter Atta ants and their close relatives invite comparisons with human farms. Both kinds of farmers do things that look unsustainable, such as growing single crops at a vast scale and applying pesticides. Yet the ants have managed to persist for millions of years.
Biologists have long mused about whether we humans can make our farms more robust by imitating the practices of ants and other small farmers. That question sounds especially pertinent when human agriculture is heading for big challenges, such as predicted population growth and climate change.
How to learn from ancient farmers isn’t an easy question though. Evolution hones by competition, not design, so there are some goofy tactics out there among the insect marvels. Now is a great era for such discussions, because researchers are paying more attention to smaller, odder insect farms. Scientists have barely begun to explore the ways beetles grow fungi, or the quirks of the ants that grow their own plants.