Figure 4.

Comparison of attachment stresses at different levels between dock beetles (Gastrophysa viridula) and Tokay geckos (Gekko gecko). Filled symbols indicate friction, and open symbols depict adhesion per (a) ‘real’ or (b) projected contact area, respectively. Ellipses highlight comparable measurements at the same level of attachment. The † labels denote adhesion measurements taken in the presence of shear forces. The two species differ by four orders of magnitude in body mass (dock beetles weigh ca 10 mg and Tokay geckos up to 100 g). Both frictional and adhesive stresses decrease considerably from the single-seta to the whole-body level for G. gecko, but remain approximately constant for G. viridula, suggesting that it is difficult for large animals to distribute load uniformly across the adhesive pad contact area, while small animals may be able to achieve a uniform load distribution. While gecko pads generate significantly larger stresses per unit real contact area, the difference disappears when attachment forces are normalized for projected contact area, i.e. the area the animals can effectively use for adhesive footpads. This indicates that gecko pads are not more efficient than beetle pads, despite having much smaller contact sizes (see §§3e, 7c). Details on the sources and calculations underlying this plot are found in the electronic supplementary material.