Body and brain changes between solitarious and gregarious locusts. (A) Differences in colouration and body size and shape in final larval instar and adult solitarious and gregarious locusts are shown. (B) Differences in brain size and proportions of particular regions in solitarious (left) and gregarious (right) brains of adult locusts are shown. Data from . Regions in the midbrain (MBr) include the olfactory antennal lobe (AL) and three neuropils in the mushroom body: the olfactory primary calyx (pcx), the gustatory accessory calyx (acx) and the multimodal lobes (lb). The optic lobe (OL) comprises three successive visual neuropils: the lamina (la), the medulla (me) and the lobula (lo). Absolute total brain size is 27% larger in gregarious locusts. The remaining numbers refer to the differences in proportions of different brain regions relative to total brain size. Positive numbers indicate that a region is disproportionally larger in gregarious locusts than in solitarious locusts (**P < 0.01; *P < 0.05; +P < 0.1).