Spider weight dragging and lifting mechanics

Abstract

© 2017 Springer Science+Business Media B.V. Spiders can produce different types of silk for a variety of purposes, such as making webs for capturing prey, sheets for wrapping, anchorages for connecting threads to surfaces, nest-building, cocoons for protecting eggs, dragline for safe locomotion and ballooning. An additional mechanism, only recently video recorded and never discussed in the literature, is spider weight lifting. Of conceptual importance comparable to that of other key spider mechanisms such as ballooning, spider weight lifting—preceded by a dragging phase for vertical alignment of weight and anchorage—is studied here. It emerges as a smart technique, allowing a single spider to lift weights in principle of any entity just using a tiny pre-stress of the silk. Such a pre-stress already occurs naturally with the weight of the spider itself when it is suspended from a thread. Large deformations, high ultimate strain, nonlinear stiffening, re-tensioning of the silk fibers and extra height of the anchoring points are all characteristics of empirical spider silk and of this lifting technique. It will be demonstrated that they all help to increase the efficiency of the mechanism. Toy experiments inspired by the spider lifting are finally proposed and compared with the theory.