Individual-level, context-dependent handedness in the desert locust.

Despite evidence of asymmetries in insect sensory perception and motor control, there is no direct evidence for functional left-right asymmetry in their limb control--handedness--equivalent to that of vertebrates such as humans (reviewed in [1,2]). Here, we show that locusts are biased in the forelimb they use to reach across a gap in the substrate upon which they are walking. The strength of this bias differed among individuals, as did the forelimb, some locusts favouring their right forelimb more often, others their left. In contrast, the locusts' forelimb movements immediately prior to reaching, or whilst walking, were unbiased. This pattern was repeated when the gap was replaced with a glass platform; forelimb use was unbiased when stepping onto the glass surface but biased when stepping onto the other side. Thus, locusts show handedness during targeted forelimb placement, but not whilst walking, the switch initiated by visual inputs. This handedness is context-dependent and is expressed by individuals rather than at the population level.