Flying spiders: What is the drag acting on a spider-dragline in free-fall?

Many species of spiders travel by using a remarkable aerial dispersal “ballooning”, which allows them to reach distances as far as 3200 km and heights of up to 5 km. Despite the many observations of spider ballooning, it remains a mysterious phenomenon due to the limited scientific observation of spider ballooning in the field, high uncertainties of the meteorological conditions, and insufficient controlled laboratory experiments. As a result, the mechanics of the three phases of the spider ballooning – takeoff, flight, and terminal – are not well-established.To shed some lights on the terminal phase, experiments using spheres of different masses and thin threads to simulate the spider-dragline were carried out. Under controlled conditions,each trial was recorded in free-fall using a high speed camera, and the displacement of the spider-dragline was tracked. This data are used to examine the effects of mass on the terminal velocity and how the Reynolds number (based on the spider diameter) affects the terminal velocity. Experimental results from controlled laboratory settings are expected to facilitate an improved understanding of the terminal phase of spider ballooning and inform future experiments and numerical models.