Hemolymph pressure-mediated friction in the tarsus of the desert locust (Schistocerca gregaria)

Abstract

The desert locust (Schistocerca gregaria) performs high-acceleration jumps within milliseconds, relying not only on powerful muscles and spring-loaded hindlegs, but also on precise tarsi-substrate interactions. Although the mechanics of jumping have been extensively studied, the mechanisms enabling rapid attachment and detachment remain poorly understood. Here, we characterize the frictional properties of hindleg tarsi under controlled low-speed contact conditions targeting selected loading features associated with jumping. We hypothesize that locusts coordinate tarsal cuticular structures with internal hemolymph pressure to modulate contact mechanics. Using high-speed videography, a suite of advanced microscopic techniques, biomechanical experiments, and biomimetic prototypes, we provide evidence that hemolymph pressure modulates tarsal stiffness and acts together with structural asymmetry to produce direction-dependent frictional responses. This interplay may contribute to adaptive friction tuning associated with jumping. Our findings advance the understanding of locust locomotor biomechanics and suggest design principles for robotic systems requiring rapid and controllable surface engagement.