Collective motion and cannibalism in locust migratory bands.
Plagues of mass migrating insects such as locusts are estimated to affect the livelihood of one in ten people on the planet [1]. Identification of generalities in the mechanisms underlying these mass movements will enhance our understanding of animal migration and collective behavior while potentially contributing to pest-management efforts. We provide evidence that coordinated mass migration in juvenile desert locusts (Schistocerca gregaria) is influenced strongly by cannibalistic interactions. Individuals in marching bands tend to bite others but risk being bitten themselves. Reduction of individuals' capacity to detect the approach of others from behind through abdominal denervation (1) decreases their probability to start moving, (2) dramatically reduces the mean proportion of moving individuals in groups, and (3) significantly increases cannibalism. Similarly, occlusion of the rear visual field inhibits individuals' propensity to march. Abdomen denervation did not influence the behavior of isolated locusts. When within groups, abdominal biting and the sight of others approaching from behind triggers movement, creating an autocatalytic feedback that results in directed mass migration. This "forced march" driven by cannibalistic interactions suggests that we need to reassess our view of both the selection pressure and mechanism that can result in the coordinated motion of such large insect groups.
Bazazi
Sepideh
S
Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, United Kingdom.
Buhl
Camille
C
Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, United Kingdom; School of Biological Sciences, The University of Sydney, Heydon-Laurence Building A08, Sydney NSW 2006, Australia.
Hale
Joseph J
JJ
Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, United Kingdom.
Anstey
Michael L
ML
Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, United Kingdom.
Sword
Gregory A
GA
School of Biological Sciences, The University of Sydney, Heydon-Laurence Building A08, Sydney NSW 2006, Australia.
Simpson
Stephen J
SJ
Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, United Kingdom; School of Biological Sciences, The University of Sydney, Heydon-Laurence Building A08, Sydney NSW 2006, Australia.
Couzin
Iain D
ID
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544. Electronic address: icouzin@princeton.edu.
D000005:Abdomen / Q000294:innervation; D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D002190:Cannibalism; D006110:Grasshoppers / Q000502:physiology*; D008465:Mechanoreceptors / Q000502:physiology; D012919:Social Behavior; D014785:Vision, Ocular / Q000502:physiology