Army ants


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.)


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