[Intro]
When humans first domesticated plants about 12,000 years ago, gotta say, it was a pretty
big deal.
But it was not a first!
Hundreds of ant species -- along with some termites and beetles -- have been farming
for tens of millions of years.
Ants practice two forms of farming: some species farm fungi, and others farm aphids.
In both cases, it’s a symbiotic relationship -- where two species have some kind of interaction
-- but more specifically, it’s mutualism, where they both benefit from that relationship.
The fungi and aphids can digest things the ants can’t, so they provide the ants with
nutrients, and in exchange, the ants protect and feed them.
There are more than 200 species of ants that farm fungi, and they’ve been doing it for
up to 50 million years.
Most of them use dead plant material, like leaf-litter, to cultivate their farms.
It’s easier for the fungi to digest that dead stuff using enzymes that break it down
into nutrients that the ants can then eat.
But dead-leaf-eating fungi usually can’t provide enough food for an entire colony,
so the ants have to go eat other stuff too.
But over the last few million years, leafcutter ants and their fungus farms have come up with
a better way: they use freshly cut, living leaves, which are more nutritious for the
fungus.
Along the way, the fungus evolved to grow nutrient-rich clusters called gonglydia, which
the ants eat.
And the ants have lost a lot of their ability to digest anything else.
You’ve probably seen pictures like this one, of leafcutter ants hauling leaves, but
they don’t actually eat those leaves.
Instead, they chew them up and spit them back out to feed the fungus gardens.
Smaller worker ants start the process at the top layers of the garden, breaking the leaves
into millimeter-size bits.
But the ants need to help the fungus digest the fresh leaves, because the thinner top
layer of the garden is the one doing the digesting, and it doesn’t have enough enzymes to complete
the job.
So they poop and spit on it.
Ants in lower sections of the nest eat some of the fungus, including its enzymes.
Those areas are more densely packed, so they have plenty to spare.
Once they’ve had their fill, they travel back up to the top and excrete enzymes onto
the leaves, in the form of saliva and feces.
Some fungi-farming ants also grow antibiotic-secreting bacteria that rid the fungi of parasites -- in
other words, the ants use pesticides on their farms!
But for some ants, fungus isn’t their crop of choice.
Instead, they farm aphids, tiny insects that feed on plant juices, almost like how humans
herd cattle.
Aphids eat phloem, the part of a plant that transports sugar, and they excrete a waste
product known as honeydew.
Honeydew is full of all kinds of sugars, like glucose and fructose, and ants tend to prefer
aphids whose honeydew also contains more complex sugars called trisaccharides.
The ants keep groups of aphids in herds above ground on plants, and all they have to do
to get the aphids to produce some honeydew is stroke them, like they're milking a cow.
And they’ll go to some extreme lengths to protect their sugary food.
The ants will keep the aphids sheltered from rain -- building structures from leaves -- and
they’ll move them to better feeding plants to maximize honeydew production.
They’ll also attack ladybugs, which love to feed on aphids, if they get too close -- even
seeking out and destroying ladybug eggs.
On the other hand, ants have been known to bite the wings off of aphids to keep them
from leaving, and they secrete some chemicals that stunt wing growth and others that slow
aphids down.
But this could be less of a trap and more of a signal to aphids, basically saying: if
you stay here, ants will protect you!
It’s a win-win for the colony of tiny farmers and for their herd.
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