Locusts

Locusts demonstrate density-dependent collective behavior at the macroscale. Solitary-phase locusts are drab, cryptic, and avoid each other. When population density increases due to favorable conditions, locusts undergo density-dependent transformation into gregarious phase - they become brightly colored, form massive swarms, and migrate long distances.

The transformation is triggered by tactile and olfactory cues reflecting high density. This density-dependent collective behavior creates locust plagues that can devastate agriculture. It represents quorum sensing at macroscale: individuals integrate signals reflecting population density and undergo coordinated behavioral and morphological changes.