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 the ants were not eating the leaves, as thousands before him had supposed — in fact, they were feeding them to something: fungi.
By Tom Brown
Belt was the first Westerner to record ant agriculture, an evolutionary pattern which had begun millions of years ago. He was one of the first to observe that leafcutter ants use leaves as fertilizer instead of eating them, and their knowledge of agriculture would still be puzzling humans nearly 160 years after Belt’s adventures.
Ants got busy farming 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 to cultivate fungi to sustain their population, in a similar way that humans do with crops today, according to recent research from the Smithsonian Museum of Natural History.
Ants can teach us a lot about our own agriculture, researchers say. “We worry constantly about antibiotic resistance. And we’re sure that also occurs in the ant system, but somehow the whole thing has been sustainable over millions of years,” said Ted Shultz, biologist at the Smithsonian Institution. “It’s hard to imagine we couldn’t learn something about agriculture and medical strategies through studying these creatures.”
Ants adapted to cultivate fungus “gardens” without the need of sunlight, regularly feeding off the produce over millions of years. The fungi grow fruiting bodies called leucoagaricus gongylophorus — which the ants are fond of eating — the same way humans might pick apples from an orchard.
It’s not uncommon for predators to diversify their food, or for animals to protect a tree where fruits grow. But ants are different — as well as rationing the food, they deliberately spread it and cultivate it, protecting it as a source of food from other fungi and parasites.
Almost 250 species of ants are farming fungi today, with the leafcutter ants being the most famous. Some even use fungi for construction purposes, turning them into buildings to support their colonies. Humans have recently begun exploring fungus as a building material on Mars, as the material is easier to grow in low gravity.
Ants and fungi also work together during warfare — especially when targeting termites. When ants attack a termite mound, they often leave it open to fungal infections, disrupting the colony and making it vulnerable to further ant raids.
But ants’ relationship with fungi may go back even further. Fungus grows inside an ants mouth, allowing it to digest food — suggesting that the ant-fungi relationship might even precede the dinosaurs.
Even now, millions of years after ant agriculture began, ants continue to farm these fungi, the Smithsonian research found. 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.”
Like a human garden would fail if they did not store seed for the next year — when a daughter queen flies to start a new nest, she carries part of the fungi with her and takes care of her garden for months before her nest matures.
When the queen’s worker ants get busy, they plant spores the same way we would plant seeds. They weed. They use fertilizer. And they have to worry about pests.
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.
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,” Schultz said.
Researchers are beginning to better appreciate how many plants, fungi 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.
(Graphics by Niall Brown)