Meeting Abstract

22-5   14:30 - 14:45  Nailing the landing: Secrets of how springtails land upright on water Ortega-Jimenez, VM*; Bhamla, S; Georgia Institute of Technology; Georgia Institute of Technology ornithopterus@gmail.com http://ornithopterus.com

Springtails (Collembola) are a diverse and abundant taxon of soil dwellers, well known for their superior jumping abilities. Most research so far on springtails has centered around their jumping biomechanics. However, landing, which has been considered uncontrolled, has not received much attention. In this talk, we will describe our discovery of how semi-aquatic springtails (Isotomurus retardatus) consistently land on the water surface with an upright orientation 85% of the time (n=20), regardless of their initial spinning rate. This near-perfect landing enables them to be in a ready position to take-off again. We observe that the springtails adopt two key principles for nailing a perfect landing. First, they adopt a U-shape posture that enhances self-righting through aerodynamic drag. Using a vertical wind tunnel (flow speed up to 1 m/s) we confirm that living springtails indeed actively change their body posture to self-right in mid-air. Second, springtails shift their center of mass downwards by trapping water (~3% of the body mass) on their collophore, a hydrophilic tube-like structure on their bodies. Using physical models of falling plates of varying geometries, we confirm that indeed small droplets placed strategically improves both self-righting, while reducing bouncing upon impact. We also conduct Particle image velocimetry (PIV) and superficial wave analysis during jumping and landing to reveal how springtails transfer momentum to the fluid. Energy dissipation to the flow through attachment of the collophore is analyzed. Our work sheds insight into the extraordinary biofluid dynamics of collembolans, that curiously derive their name from the peg-like collophore structure rather than the springtail, offering insights into its biological function for landing, that could inform future micro-scale jumping robots.