When the asteroid that killed the dinosaurs hit the Earth, the sky went dark for months. Without sunlight, plants died, and the whole world started to rot. And in the middle of all that rot, a few ants did something no animal had ever done. They started farming.
Humans have farmed for about 12,000 years. Ants have done it for about 66 million. In that time, they've learned to grow crops, plant gardens and raise livestock, the same three things human farmers do.
The first crop: fungus
The ants' first crop wasn't a plant. It was a fungus, the same kind of living thing as a mushroom.
In 2024, Ted Schultz and his team at the Smithsonian figured out when this started. They compared the DNA of 276 kinds of ants and 475 kinds of fungus. DNA changes slowly over time, so the differences work like a clock. That clock pointed to about 66 million years ago, right when the asteroid hit. With dead plants everywhere, fungus that eats dead plants grew like crazy, and some ants started collecting it and growing it at home.
About 27 million years ago, one kind of fungus became fully domesticated. That means it changed so much from living with ants that it can't survive in the wild anymore, just like corn can't grow without human farmers. Today, nearly 250 kinds of ants in the Americas farm fungus.
The most famous are leafcutter ants. They don't eat the leaves they carry. They chew them into mush and use it to feed underground fungus gardens, then eat the fungus. One nest can go more than 6 metres deep, be as wide as a tennis court, and hold millions of ants. All that farming makes a lot of waste, which we cover in Leafcutter Ants Have a Greenhouse Gas Problem.
From fungus to plants
Fungus grows in the dark, underground. But some ants found a way to farm in the sunlight, high up in the trees. Instead of growing fungus, they grow plants.
On the islands of Fiji, an ant called Philidris nagasau grows at least six kinds of Squamellaria, plants that live on tree branches instead of in soil. Guillaume Chomicki and Susanne Renner watched the ants collect the plants' seeds, push them into cracks in the tree bark, and then fertilize the baby plants with their own poop.
The ants aren't doing this to eat the plants. They're building houses. As each plant grows, it swells into a hollow ball, and the ants move in. One colony can spread across several trees, with the queen in the middle and ant trails linking the plant-houses like roads between towns. The ants and plants now need each other so much that neither can survive alone. The researchers think they've been partners for about 3 million years.
Other ants use plants the same way, as building material. In Malaysia and Sumatra, the irritable carpenter ant, Camponotus irritabilis, is one of the most aggressive ants in the world, and it builds its own homes in the treetops. The ants make walls out of carton, a kind of homemade paper made from chewed plant fibres and waste. Then they plant the seeds of a vine called Hoya elliptica in the walls. As the vine grows, its roots hold the nest together and tie it to the tree.
But the ants stay in charge of the design. They bite off roots that take up too much space, only fertilize certain parts of the nest, and carry seeds to one "growing zone." The vine becomes the frame of their house, shaped by the ants like a hedge shaped by a gardener.
A farm with two families
Running a big farm is a lot of work, and some ants share the job with another species. In Borneo, two different ants live in the same nest: a small acrobat ant, Crematogaster modiglianii, and a large carpenter ant, Camponotus rufifemur.
The acrobat ants usually start the nest, and the carpenter ants move in. They forage side by side but raise their babies separately, like two families sharing one house. Each side brings a skill. The small acrobat ants are better at finding food, so the carpenter ants follow their scent trails. The big carpenter ants are better fighters, so they defend the nest. The carpenter ants have never been found living without their partners.
From plants to animals
Growing crops is only half of farming. The other half is raising animals. And ants do that too.
Choosing which animals to raise
Many ants raise aphids, tiny bugs that suck sap from plants and give off a sweet liquid called honeydew. The ants protect the aphids and drink the honeydew, a lot like people keeping cows for milk. Our aphid farming story explains the basics. But in Japan, one ant goes further. It controls which aphids its herd is made of.
The Japanese garden ant, Lasius japonicus, raises a mugwort aphid that comes in two colours. Green aphids make better honeydew, but red aphids have babies faster. Left alone, the red ones take over. Saori Watanabe and her team found that the ants protect mixed herds the most, especially ones that are about 65% green. With ants around, the green aphids have babies just as fast as the red ones. The ants don't just guard their herd. They keep it the way they want it.
A ranch inside a tree
The strangest ant ranchers live somewhere almost no other ant can: inside living trees. In Africa, the tiny blind ant Melissotarsus, only about 2 mm long, chews tunnels through healthy wood. Its jaws have zinc built into their tips to make them strong enough. It's also one of the only ants that can spin silk as an adult, and it uses the silk to seal its tunnels.
Its legs are made for tunnelling, not walking, so a colony spends its whole life inside one tree. In the tunnels, it keeps huge herds of armoured scale insects, tiny sap-suckers that usually hide under hard shells. These insects don't make honeydew at all. Christian Peeters and his team think the ants live off the wax the scale insects give off, the skins they shed, and the ones that die. The scale insects living with the ants have even lost their shells, because the ants protect them instead.
What 66 million years of farming teaches us
From fungus to vines to tiny livestock, ants have been farming since the age of the dinosaurs ended, through mass extinctions and big changes in climate. Their farms aren't perfect. They depend on just a few crops, and they can fail. But they've kept going about 5,000 times longer than ours have.
Maybe the most useful lesson from ant farmers isn't how much they grow. It's how long they can keep growing it.
Further reading
- Schultz, T. R. et al. (2024). The coevolution of fungus-ant agriculture. Science.
- Chomicki, G. & Renner, S. S. (2016). Obligate plant farming by a specialized ant. Nature Plants.
- Weissflog, A., Kaufmann, E. & Maschwitz, U. (2017). Ant gardens of Camponotus irritabilis and Hoya elliptica in Southeast Asia. Asian Myrmecology.
- Menzel, F., Linsenmair, K. E. & Blüthgen, N. (2008). Selective interspecific tolerance in tropical Crematogaster–Camponotus associations. Animal Behaviour.
- Watanabe, S. et al. (2016). Color polymorphism in an aphid is maintained by attending ants. Science Advances; Watanabe, S. et al. (2018). Scientific Reports.
- Peeters, C. et al. (2017). A mutualism without honeydew: what benefits for Melissotarsus emeryi ants and armored scale insects? PeerJ.
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