Ant Rafts and Other Water Repellent Systems

Abstract

We present a series of experiments demonstrating the water-repellent adaptations of a range of animals, from insects to mammals. These adaptations are necessary for survival in rain and other wet environments. During flash floods, fire ants weave hydrophobic rafts with their own bodies in order to keep their colonies dry. We discuss their method of self-assembly and present a model that predicts their construction rate. To survive raindrop impacts, flying insects take advantage of their low mass, which prevents drops from splashing on them. The resulting impact force on flying mosquitoes is 100-300 gravities, quite possibly the largest in the natural world. For such small insects, small size is advantageous in rain. If an animals is large, active mechanisms must be employed to shed water. Mammals of all sizes can shake off 70% of the water on their bodies in fractions of a second. We show that wet mammals shake at tuned frequencies to dry and present a scaling law relating animal size and frequencies required to dry. In this talk, the audience will learn the basics of modeling and experimentation with surface-tension phenomena.