Fig. 1. Schematic of the nine stages of phase change analysed. Shown descending on the left-hand side, cohorts of long-term crowded (gregarious-phase; stage 1) locusts are taken and isolated for increasing periods, becoming increasingly solitarious. Locusts that have been isolated for three whole generations (long-term solitarious; stage 6) are then taken and crowded for increasing periods, causing a progressive change to the gregarious phase, shown rising on the right-hand side. Locusts that are crowded for long enough revert to the gregarious phase state.