Workers hook their tarsal claws into one another and build a hanging mass roughly a metre across, containing chambers and passages. Temperature inside is regulated by the ants loosening or tightening the structure. The queen and the developing brood sit at the centre. In the morning the bivouac dissolves and the colony moves.
The cycle is driven by brood. Eciton alternates a nomadic phase, when the colony emigrates almost nightly and raids heavily to feed a large cohort of larvae, with a statary phase of two to three weeks when larvae pupate, the queen lays a new batch, and the colony stays put. The rhythm is internal, keyed to brood development rather than to weather.
Raids fan out as a swarm front rather than a column, flushing insects, spiders and small vertebrates. Antbirds follow the fronts to catch what flees, and dozens of other species, including flies and butterflies, specialise on army ant swarms. The ants themselves eat almost entirely arthropods; accounts of columns consuming livestock belong to fiction.