Sensory deprivation experiments in the field. (A) A marching band of S. gregaria photographed in Kenya in 2020. (B) (i) Locust bands in a total of 112 locales between 27 February and 12 March of 2020 in the Samburu and Isiolo districts of Kenya. Scale bar: 15 km. (ii) Observed marching band directions. n = 56 bands. Histogram counts: min = 2, max = 23. (C) Single tagged locusts were reintroduced to a marching band after antennectomy (Olfaction−, n = 89) or visual occlusion (Polarized Vision−: dorsal eyes and ocelli, n = 54; Vision−: complete eyes and ocelli, n = 114). Control n = 110. Locust movements were reported as mean vectors. Statistical annotations on each upper right corner stand for the results of Rayleigh test for nonuniformity. (D and E) Mean binarized Euclidean distance (Activity) and mean vector magnitude in congruence with marching band (Marching) by control and treated animals. Olfct, olfaction; PolVis, polarized vision; Vis, vision. See table S2 for statistical summarie.
Material
Abstract
Collective motion, which is ubiquitous in nature, has traditionally been explained by “self-propelled particle” models from theoretical physics. Here we show, through field, lab, and virtual reality experimentation, that classical models of collective behavior cannot account for how collective motion emerges in marching desert locusts, whose swarms affect the livelihood of millions. In contrast to assumptions made by these models, locusts do not explicitly align with neighbors. While individuals respond to moving-dot stimuli through the optomotor response, this innate behavior does not mediate social response to neighbors. Instead, locust marching behavior, across scales, can be explained by a minimal cognitive framework, which incorporates individuals’ neural representation of bearings to neighbors and internal consensus dynamics for making directional choices. Our findings challenge long-held beliefs about how order can emerge from disorder in animal collectives.