Ballooning in spiders: results of wind tunnel experiments

Abstract

Ballooning refers to the aerial displacement of spiders made possible by friction between rising air and strands of silk. The phenomenon is widespread in the order Araneae and is thought to be the primary means by which spiders disperse over long distances. Only recently have attempts been made to understand the aerodynamic constraints under which ballooning spiders must operate. The current study was stimulated by the cogent theoretical work of HUMPHREY (1987), and provides the first empirical data on the physical forces acting on spiders about to become airborne and on those that are already airborne. The data indicate (1) that both the silk and the spider's body provide the drag necessary for ballooning, (2) that fluid dynamic models overestimate the difficulty of becoming and remaining airborne, (3) that the spider has both postural and silk length control over drag development, (4) and that only very small spiders can rely on ballooning for dispersal over long distances.