Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.25.266163v1?rss=1 Authors: Loveless, J., Garner, A., Issa, A. R., Webb, B., Ohyama, T., Alonso, C. Abstract: All animal movement must ultimately be governed by physical laws. As a basis for understanding the interactions between the nervous system, musculature, body mechanics and the environment that govern behaviour in the fruit fly larva, we here develop an effective theory for the physics of its motion in three dimensions. We start by defining a set of fields which quantify stretching, bending and twisting along the larva's anteroposterior (AP) axis. We then perform a search in the space of possible physical theories that could govern these fields, by using symmetry considerations, stability requirements and physical reasoning to rule out possible terms in our theory's Lagrangian (which governs its energy-conservative physics) and Rayleigh function (which governs its energy-dissipative physics). We restrict attention to the physics that dominates at long-wavelengths, which allows us to arrive at a unique, simple theory of the larval midline, governed by a minimum of phenomenological parameters that capture both purely biomechanical as well as neuromuscular effects. Owing to the simplicity of our theory, we are able to derive most of our results analytically. The model makes strong quantitative predictions for the dynamics of peristalsis, rolling, and self-righting, and also successfully predicts statistical properties of these behaviours and of unbiased substrate exploration. Copy rights belong to original authors. Visit the link for more info