Figure 6.

Adhesion per unit projected contact area measured with and without shear force for a Tokay gecko with dry and hairy adhesive pads (Gekko gecko, from [129]), a dock beetle with hairy and wet adhesive pads (Gastrophysa viridula, from [107,137]), an Indian stick insect (Carausius morosus, from [108]), a cockroach (Nauphoeta cinerea, from [144] and Y. Zhou 2014, unpublished data), and a tree frog (Litoria caerulea, from [145] and N. Crawford 2014, unpublished data), the latter three all with smooth and wet adhesive pads. In all species, adhesive stress increases considerably when shear forces are applied to the pads prior to detachment. Note that the shear-induced adhesive stress shown here might increase even more for higher shear forces (see §7b) and that the magnitude of shear forces differed between the experiments, so that a comparison between the species has to be interpreted with care.