Fig. 9. (A) Typical surface profiles of the structures used in experiment 2, determined using a contact-profilometer. The roughness is characterized by Ra, defined as the arithmetic mean of the deviations from the base line measured over an evaluation length (DIN EN ISO 4287). The mean diameter of the grains deposited on the abrasive paper used for experiments 2A, 2B and 2D (compare Table 1) is 270 µm, the sand glued to the channel ground had a mean diameter of 200 µm. In contrast to the abrasive paper the sand grains are deposited next to each other without gaps. (B) Dorsal view of a tarsus of Cataglyphis fortis (ar, arolium; cl, tarsal claws). Tarsal claws are separated from each other by approximately 320 µm. (SEM micrograph courtesy of Andrew Martin.)