Eciton army ants have a bi-phasic lifestyle where they alternate between a nomadic phase and a stationary stage. In the stationary or statary phase ('statary' is an old English word meaning "to stand in place"), which lasts about three weeks, the ants remain in the same location every night. They make a nest out of their own bodies, protecting the queen and her eggs in the middle. This temporary home is known as a bivouac. In the nomadic phase the ants move their entire colony to a new location nearly every night for two weeks.
When the ants first enter the statary phase, the queen's body swells massively and she lays as many as 250,000 eggs in less than a week. While the eggs mature, the ants swarm with less frequency and intensity. When the eggs hatch, the excitement caused by the increased activity of the larvae causes the colony to enter the nomadic phase. The colony swarms much more intensely and nearly every day, and the ants move to a new location every night. After two weeks, around the time when the larvae begin to pupate, the colony again enters the statary phase, and the cycle begins anew.
Because of the regularity and intensity of E. burchelli and E. hamatum swarms, many insect, bird and butterfly species have evolved complex relationships with these ants. There are butterflies that lay their eggs on insects disabled by the ants. There are ant-mimicking staphylinid beetles, shaped like the ants they follow, that run with the swarm preying on stragglers or other insects injured or flushed by army ant activity; and there are some insects that spend their entire lives hidden in Eciton colonies mimicking ant-larvae. There are also more than 10 species 'ant-birds' that rely on the ants partially or completely for their food. Some of these birds actively check army-ant bivouacs each morning, follow the foraging trail to the swarm front, and prey on insects fleeing the ants.
An E. burchelli bivouac hidden under a fallen tree. Notice the tower of ants that connect the bivouac to the ground. Army ants commonly use their own bodies to build bridges and smooth out trails. This column of ants was probably 16 inches tall and more than an inch thick.