Insect Farmers

By Paula E. Cushing
Photos by Jim Wetterer, Columbia University

Forget about picnics. These ants grow their own food.

The farmer stepped back and surveyed her garden. It looked fine and healthy. A little more fertilizer here and there and her day’s work would be done.

Her sisters were busy in another part of the garden gathering some of the crop to feed to the youngsters. Yes, nothing beats a good garden of young mushrooms.

You see, this is no ordinary farmer. She is a leaf-cutting ant.

I first saw leaf-cutting ants on a six-month visit to Panama. I had plenty of time to watch the ants because I lived and worked at a tropical research station on Barro Colorado Island in the Panama Canal area.

Barro Colorado became a biological reserve in 1923. Since then scientists from all over the world have gone there to study tropical plants and animals.

Jungle Walks
There are no roads on the island, just nature trails cutting through the jungle. Nearly every time I walked out on the trails, I had to step over a marching column of leaf-cutting ants—they seemed to be everywhere!

At first, the marching columns looked like little pieces of leaves moving by themselves. But when I looked more closely, I saw that each piece of leaf was being carried by a reddish ant many times smaller than the leaf. The ants had cut the leaves with their scissorlike jaws and were carrying them back to their nests.

A big worker ant cuts out a piece of leaf while smaller workers guard her from harm. The guards then ride on the piece, protecting their larger sister all the way home. a

Leaf cutters don’t eat the leaves. Rather, they use the leaves to raise their most important food, which is a particular kind of fungus.

The ants take the leaves to special rooms in their underground nests. They cut the leaves into smaller pieces, chew the pieces until they are wet and spongy, and deposit them in their garden.

Then the ants transplant some fungus onto their fresh “leaf-soil.” Sometimes they add fertilizer that they excrete from their abdomens.

Adult ants feed on this fungus as well as on sap. The fungus is also eaten by the larvae, which are the baby ants.

The fungus they grow is a type of mushroom. But the ants have been farming it for so long that it doesn’t grow into anything that looks like regular mushrooms. Instead, it looks more like a mass of tiny double-headed lollipops.

Ants, Big and Small
A leaf-cutter colony is made up of ants of different sizes. Large ants go out and gather the leaves. Smaller ants guard the big ants, cut up the leaves, tend the garden, and care for the eggs and larvae.

The biggest ant is the queen. Her job is to lay eggs. All of the other ants in the colony are her daughters. They have many jobs, which they do by instinct, communicating with one another and their queen when necessary.

Of course, ants can’t talk the way we can. Instead, the ants communicate through a chemical language. They pass around their chemical messages when they feed one another. Workers pass droplets of food to other workers (their sisters). They also feed larvae. Larvae sometimes feed their nurses. The queen feeds her daughters. And the workers feed their mom, the queen. An ant colony’s chemical communication network is more complicated than our telephone lines.

City of Ants
A three-year-old leaf-cutter colony can have as many ants as there are people in Washington, D.C. It can be as deep as three tall men standing on one another’s shoulders.

Despite the size of the nest, the air inside stays cool and fresh because the ants build their own type of air-conditioning system.

The fungus gardens are in the center of the nest. The air there is warm because of the growth of the fungus and the activity of the ants tending the gardens.

This warm air rises and leaves the nest through air shafts above the gardens. The movement of hot air sucks cooler fresh air into the nest through air shafts built at the edges of the nest, away from the gardens.

And to think that this enormous nest with its millions of ants all began with one individual, the queen.

The queen sits on her garden of fungus. She is much larger than the workers.

New Colonies
As time passes, a leaf-cutter colony produces special larvae that turn into new queens and males, which are called drones.

These ants have wings, and they fly away from the colony to mate. The males die after mating, but the females land, shed their wings, and begin their own nests.

But before each new queen leaves her old nest, she swallows a bit of fungus. After a newly mated queen lands, she builds a small, one-room nest. To start the new fungus garden, she lays eggs, crushes them, and spits the wad of fungus onto them.

After the fungus has spread, she lays more eggs. In six to eight weeks, her daughters are ready to tend the garden and care for their baby larval sisters.

Then the queen stops puttering around the garden and concentrates on laying eggs and watching her industrious daughters tend the family business.