Ants are little, but there are a lot of them! If you could put all the ants in a tropical rainforest onto a scale, they would weigh more than all the animals with backbones there.
Because there are so many of them, and because they are often partners with other plants and animals, they are very important in rainforests. Here is some information about how two kinds of ants live.
Here come the army ants. If you are an insect, look out! Thousands of ants may be in the column of raiders that is advancing through the rainforest, pinning down and cutting up every small creature that cannot get away. The swarm changes shape as it advances, but it may fan out as it moves until it is as wide as 100 feet at the front. In the 1930’s work done at the Smithsonian Tropical Research Institute pioneered the study of army ant ecology and behavior.
Army ants don’t spend all their time on raids like this.
They move through the forest on about a 35 day cycle. They will stay in one place for almost three weeks, sweeping out the area around the always temporary nest. Eggs are laid during this time.
After these eggs hatch, producing larvae, the raids begin – to feed the hungry young.
These raids may last a couple of weeks. When the ants are on a raid, the column advances by day. At night, they again create their temporary nest called a bivouac. To build the nest the ants hook their claws together so their bodies form a living shield. Inside, the larvae and queen are kept safe. The army ants spend each night that way, and then in the morning they move on. Once the larvae change into nonfeeding pupae the cycle begins again.
This is how the army ants make sure that they can successfully raise their young. But as is typical in rainforests, the lives of other species are connected with those of the ants.
For example, there are beetles, wasps, and millipedes that imitate the smell of the army ants. Ants don’t see well. They communicate with each other mostly by smell. So when these other insects imitate the army ant smell, the ants think these strangers are part of the swarm and do not attack them. That way these other insects can safely do the eating without doing the hunting of army ant prey.
The best known camp followers are the antbirds. Sometimes as many as ten different kinds will follow a column of army as ten different kinds will follow a column of army ants, flying along the front of it. These birds do not eat the ants, but feed on insects the ants have caught and on insects that are trying to escape from the ants. Some are professional antfollowers, highly dependent on swarms and seldom found away from them.
The chain of connection goes even further. There are butterflies that flutter around army ant columns. What they are interested in is the antbirds’droppings.
Even rainforest people have found ways to use the army ants, some of which have huge pincher-like jaws. These jaws are so big and strong that Indians in South American rainforests sometimes use them to clamp wounds shut, the way our doctors use stitches. (The ant is killed after it has bitten the wound closed.)
Leaf-cutter ants live in colonies that can be huge, up to three or four million individuals, occupying as many as three thousand underground rooms.
These ants live in a partnership with a fungus that grows nowhere else in the world except in leaf-cutter ant colonies. The ants depend on the fungus and the fungus depends on the ants. The fungus has lost the capacity to reproduce on it’s own. The ants grow the fungus, feeding it pieces of leaves and flowers that they bring back, often from high up on rainforest trees. They destroy more leaves than any other insect in the rainforest.
The ants chew up the leaves for the fungus, and fertilize it, and weed out any other plants that start growing in the fungus garden. It is also the ants that start the new gardens (the fungus has lost the ability to do so by itself). When a young leaf-cutter ant queen flies off to start a new ant colony, she takes with her in her mouth a small piece of the fungus to begin a new garden.
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The ants also depend on parts of the fungus to digest their food; they feed the fungus the part of the plant they were unable to digest (the celulose). The ants, in turn, then feed on the fungus; the leaf-cutter ant larvae eat nothing but the fungus.
You can see ants carrying pieces of leaf down a tree in the rainforest. Many carry pieces so large that it would be as if you were carrying a dinning room table down a tree.
And so many of these leaves, a smaller ant is perched. Why? It acts as a guard, protecting the larger ant against a parasitic fly. This kind of fly tries to lay its eggs on an ant’s head. The larvae that hatch from these eggs would kill the ant. The ant carrying the leaf can’t protect itself without dropping the leaf, so the smaller ant rides along to act as guard.