Presenter: Laura Miller, Ph.D., University of North Carolina at Chapel Hill
Topic: The dispersal of aerial plankton: Spider ballooning and flapping with bristled wings
A vast body of research has described the complexity of flight in insects ranging from the fruit fly, Drosophila melanogaster, to the hawkmoth, Manduca sexta. Over this range of scales, flight aerodynamics, as well as the relative lift and drag forces generated, are surprisingly similar. The smallest flying insects (Re~10) have received far less attention, although previous work has shown that flight kinematics and aerodynamics can be significantly different. At a similar scale, spiders use a type of aerial dispersal called “ballooning” to move from one location to another. In order to balloon, a spider releases a silk dragline from its spinnerets and when the movement of air relative to the dragline generates enough force, the spider takes flight.
In this presentation, we have used a multi-pronged approach that consists of measurements of flight kinematics, quantification of wing morphology and dragline properties, measurements of flow velocities and forces using physical models, and direct numerical simulations to compute flow and lift and drag forces. For tiny insects, the lift to drag ratio during hovering flight decreases significantly as the Re decreases below 10. The clap and fling mechanism of lift generation does augment lift forces ~30%, however, peak drag can increase almost an order of magnitude due to viscous effects from wing-wing interaction. Bristles can reduce these peak forces, and may aid in passive flight behavior. In spiders, the dynamics of ballooning is significantly influenced by the spider mass and the length of the dragline. Dragline properties such as the bending modulus also play important roles. While the spider-dragline is in flight, the instability of the atmosphere and stratification layers may allow the spider to remain airborne for long periods of time.