Meeting Abstract

23.1  Monday, Jan. 5  Attachment forces of single adhesive setae from tarantula feet PEATTIE, A M*; FEDERLE, W; Univ. of Cambridge; Univ. of Cambridge ap557@cam.ac.uk

Spiders and geckos have convergently evolved dry fibrillar adhesives on their feet that allow them to climb smooth vertical surfaces. These two types of adhesives are materially and morphologically distinct. Gecko adhesive fibrils, called setae, are made of keratin, as opposed to arthropod cuticle. Gecko setae split many times, branching into small flattened tips (called spatulae). Spider setae are paddle-shaped, with a planar array of spatulae at a constant (~5 m) height from the seta surface. In this study we present the first attachment force measurements for single setae from the pretarsal claw tufts of a spider, the theraphosid Grammostola rosea. We mounted single setae onto pins and measured the frictional and adhesive forces generated when they attached to a glass substrate. G. rosea setae were consistently longer than all other gecko setae studied, and bore more spatulae. The mean peak shear force across all claw tuft setae was 131 N 15.7 SE (n=23 setae, 4 animals), while mean peak adhesive force was 50.8 N 5.3 SE. The apparent mean shear force per spatula was not significantly different from that of geckos, nor were their dimensions (200-350 nm wide). Contrary to previous findings in geckos, however, attachment force was not strongly predicted by the number of spatulae on a given seta in spiders. It may be that the spider seta structure is not as effective as geckos at creating maximal contact between the spatulae and the substrate. Claw tuft setae, like claws, are oriented to engage with the substrate during a pulling motion of the foot. Many spiders have additional setae on the ventral surface of the tarsus, which are oriented to engage during pushing motions. Future studies will investigate the differences among these different types of setae, as well as setae from more species and different types of surfaces.