Eciton Army Ant

Eciton burchellii is one of the most-studied army ants of the Neotropics. Like Old World driver ants (Dorylus), Eciton are fully nomadic — they build no permanent nest. Instead, the colony lives in a 'bivouac': a living mass of 150,000–700,000 worker ants that grip each other body-to-body, forming a basketball-sized cluster around the queen and brood, hanging from a low branch or log. The bivouac dissolves at dawn and the colony marches in massive raid columns up to 100 meters wide and many hundreds of meters long. Ants encountering obstacles do not detour — they construct living bridges and ramps from their own bodies. Workers position themselves head-down across gaps, grip with mandibles and tarsal claws, and other ants march across them. The bridges self-optimize: too many ants in the bridge means too few foraging, and the colony dissolves bridges that don't carry enough traffic. Raids generate enormous quantities of flushed prey — fleeing insects, spiders, lizards, and small vertebrates — and over 100 species of antbirds, antwrens, antshrikes, and tropical butterflies have evolved obligate or facultative dependence on army-ant raids. The relationship is the most species-rich animal-following community known.