Insights from Insects: Emergent Dynamics in the Physics of Animal Locomotion.

Animals, including ourselves, move through complex and uncertain environments with an ease and agility we find hard to recreate in engineered systems. Indeed the ability to move is a trait of all animals. The physics of organisms is maturing given a convergence of non-linear dynamics, soft active matter, and biophysics of complex systems, along with associated computational tools, time-resolved imaging methods, and rapid prototyping particularly in robotics. There is a long history of considering the organism in physics. Yet it remains challenging to capture the relevant details necessary to identify the interesting, often simple, dynamics that emerge at the level of the organism without just revealing in their complexity. We are making progress faster than ever, especially in understanding the physical and physiological mechanisms of locomotion. High-speed x-ray diffraction through living muscles is connecting active matter principles to the macroscopic material dynamics of this versatile actuator. The brains of small flapping insects are still complex, containing 10⁵-10⁶ neurons. Despite this complexity, we find that they control wingstroke dynamics with as little as 10¹ bits/wingstroke, mostly through precise timing that takes advantage of muscle’s nonlinearities. Analyzing and manipulating feedback pathways in animals through virtual reality is enabling a dynamic systems description of locomotion that can be surprisingly low dimensional and linear. Using robots as experimental tools to get at biophysical mechanisms, we are discovering how animals’ visual systems can adjust to light levels that vary by 7 orders of magnitude from early afternoon to late dusk. We cannot yet emulate the motility seen in nature, nor derive all behaviors, but for the physicist interested in the workings of nature’s most versatile systems, the neuromechanics of animal locomotion is an exciting opportunity.