Ant agriculture holds secrets for human sustainability
A sweaty bearded man was making his way through the 19th century Nicaraguan jungle when he stumbled upon a trail of ants.
The explorer, Thomas Belt, noticed the ants were carrying leaves. As Belt so often did on such occasions, he got out his notebook and began to draw them. When he looked closer, he saw that the ants were not eating the leaves, as thousands before him had supposed — in fact, they were feeding them to something: fungi.
Belt was the first Westerner to record ant agriculture — an evolutionary pattern that had begun millions of years ago. His observations would inspire the name the ants still have today: Leafcutter ants, and their knowledge of agriculture would be puzzling humans nearly 160 years after Belt’s adventures.
According to recent research from the Smithsonian Museum of Natural History, ant agriculture dates back to millions of years before Belt's journey. Ants got busy farming 63 million years ago — soon after the asteroid that killed the dinosaurs kicked up dust into the air, blocking out the sun and wiping out large mammals down on the earth’s surface. Ants adapted then to cultivate fungi to sustain their population, and have been doing so ever since, in a similar way that humans do with crops today.
“When you look at the timelines involved, humans are a tiny blip on that timeline,” said Ted Schultz, a biologist at the Smithsonian and the lead researcher on the study. Ants evolved around 120 million years ago — compared with 300,000 years ago for humans — and they’ve had agriculture for around half of that time.
They’ve long relied on fungi for sustenance, but the study was the first of its kind to discover that after the asteroid-induced global winter, the ants cultivated so-called fungus “gardens” without the need of sunlight. The fungi grow fruiting bodies called gongylidia, which the ants are fond of eating — the same way humans might pick apples from an orchard. In this way, the ants regularly fed off the produce over millions of years.
Even now, millions of years after ant agriculture began, ants continue to farm these fungi, the Smithsonian research found. Humans digest our food in our guts with the help of trillions of bacteria. Ants also use bacteria, but they digest their food outside of their bodies, rather than inside. There’s emerging evidence that ants use fungi the same way we use gut bacteria — fermenting the food in their fungi gardens before eating it.
Ants are very particular about their underground greenhouses, even to the point of regulating carbon dioxide levels to keep damaging bacteria away. “[The ants] remove things that don't really seem to work,” said Michael Poulsen, an ant and termite researcher at the University of Copenhagen, who was not involved with the study. “[They] have several layers of defense.”
When the daughter of a queen ant moves to a new colony, she takes the spores of the fungus garden and plants them deep underground, the same way human gardeners plant seeds. The ants weed. They use fertilizer. And they have to worry about pests.
Leafcutter ants can teach us a lot about our own agriculture, particularly how to prevent pesticide resistance. “We’re sure that also occurs in the ant system, but somehow the whole thing has been sustainable over millions of years”, said Shultz, describing how ants have found a way to stop pests building up a tolerance to drugs designed to kill them.
Bacteria colonies growing on ant exoskeletons spread to their fungi crops and protect them from parasites — similar to the way herbicides protect modern crops. The bacteria growing on the ants is known as streptomyces, and it’s responsible for many of our medicines, including breast cancer treatments. Schultz and others are trying to find out how ants use bacteria to make their food resilient to pests and parasites, and how we can do the same. “It’s hard to imagine we couldn’t learn something about agriculture and medical strategies through studying these creatures,” said Shultz
But the scientists don’t have long to complete their work. Schultz warned that ant species are at risk of disappearing as climate change threatens their interconnected habitat — and they could take hundreds of bacteria and fungal species with them.
Thomas Belt, the 19th century explorer, worked as a mining engineer in Nicaragua. Those same ants that he documented in 1874 are used today by environmental consultancies surveying mining operations, which often hire ant biologists to measure leafcutter ant colonies — they can serve as a proxy for the health of an entire ecosystem. “These are canaries in our coal mines,” said Schultz.
Researchers are beginning to better appreciate how many plants, fungus and bacteria are dependent on ants to survive, meaning their wellbeing could support hundreds or even thousands of species. Scientists are trying to learn what they can before ant secrets are lost forever.
“I’m just worried because I love these organisms,” Schultz concluded.