Adhesion measured on the attachment pads of Tettigonia viridissima (Orthoptera, Insecta)

The tarsi of the cricket Tettigonia viridissima bear flexible attachment pa ds that are able to deform, replicating the profile of a surface to which t hey are apposed. This attachment system is supplemented by a secretion prod uced by epidermal cells and transported onto the surface of the pad through the pore canals of the pad cuticle. This study shows that the secretion al one is necessary, but not sufficient, for adhesion. To account for the full adhesive force, the deformation of the pad and the resulting changes in co ntact area were considered. In two series of experiments, the adhesive prop erties of the secretion and the adhesion of the whole pad were measured usi ng a force tester, the sensitivity of which ranged from micronewtons to cen tinewtons. The adhesive forces of the secretion measured between a smooth sapphire bal l with a diameter of 1.47 mm and a flat silicon surface ranged from 0.1 to 0.6 mN. In a control experiment on the silicon surface without secretion, n o adhesive force was measured. There was no dependence of the adhesive forc e on the applied compressive force. When an intact pad was pulled off a flat silicon surface, the adhesive forc e increased with increasing applied compressive force, but it did not incre ase further once the applied force exceeded a certain value. The saturated adhesive force, ranging from 0.7 to 1.2 mN, was obtained at applied forces of 0.7-1.5 mN. The hemispherical surface of the pad had a larger contact ar ea and demonstrated greater adhesion under a larger applied force. Adhesion became saturated when a pad was deformed such that contact area was maxima l. The tenacity (the adhesive force per unit area) was 1.7-2.2 mN mm(-2).