Integrating across different levels of biological organization is a fundamental goal in ecology. Swarms of locusts and Mormon crickets are potentially devastating examples of the ways in which relatively simple interactions among individuals can scale up to complex behaviours at the group level. Importantly, animal movements can be influenced by both intrinsic and extrinsic factors. In both locusts and Mormon crickets, an individual’s intrinsic nutritional state relates to its propensity to cannibalize conspecifics. In turn, these state-dependent cannibalistic interactions among individuals play a causal role in the collective dynamics of mass movement at the group level. Nutritionally-deprived individuals must necessarily move to locate new resources, but at the same time must also keep moving in order to avoid being attacked by similarly deprived conspecifics approaching from behind. The benefits of travelling in a group of cannibals must necessarily outweigh the costs. Reduced predation risk has already been demonstrated as one such benefit.
We will present empirical evidence in support of another non-mutually exclusive benefit, the ‘lifeboat hypothesis’. By virtue of cannibalism, an individual group member can survive longer and travel farther than a solitary individual, thereby increasing its likelihood of encountering new resources while traversing a heterogeneous environment.