SUMMARY
The feet of the jumping spider Evarcha arcuata attach to rough substrates using tarsal claws. On smooth surfaces, however, attachment is achieved by means of a claw tuft, the scopula. All eight feet bear a tarsal scopula, which is equipped with setae, these again being covered by numerous setules. In E. arcuata, an estimated 624 000 setules, with a mean contact area of 1.7×105 nm2, are present. The spider's entire contact area thus totals 1.06×1011nm2. Adhesion to the substrate does not depend on the secretion of an adhesive fluid. Analysis via atomic force microscopy (AFM) shows that a single setule can produce an adhesive force (Fa) of 38.12 nN perpendicular to a surface. Consequently, at a total Fa of 2.38×10–2 N and a mean body mass of 15.1 mg, a safety factor (SF; Fa/Fm, where Fm is weight) of 160 is achieved. Tenacity (τn; Fa/A, where A is area of contact) amounts to 2.24×105 N m-2.
