Asymmetric spatula heads combined with lateral forces provide a mechanism for controlling the adhesive attachment of a range of spider species

Dry adhesion is a common strategy utilized throughout nature, allowing attachment of animals to a large range of surfaces. Crucially, it enables the animal to switch rapidly and safely between attachment and detachment in order to facilitate motion. Here we investigate the magnitude and directionality of the dry adhesion systems of a number of spider species. Atomic force microscopy (AFM) was used to measure the normal adhesion strength of a single setule. Secondly, scanning electron microscopy (SEM) was used to directly observe the interaction of a spider seta with an AFM cantilever tip and then, based on the known stiffness of the cantilever and the deflection distance, to estimate the adhesion force between them. The AFM-measured values for normal adhesion of single spider setules to a surface (9–16 nN) were similar to values predicted by the Johnson–Kendall–Roberts (JKR) model. In contrast, the force of adhesion, estimated from the SEM images, between the seta and the cantilever reached values as high...