Meeting Abstract

58.1  Tuesday, Jan. 5  Pushing and pulling: beetles use different tarsal pads to walk and climb BULLOCK, J. M. R.*; CLEMENTE, C. J.; FEDERLE, W.; University of Cambridge ; University of Cambridge ; University of Cambridge jmrb3@cam.ac.uk

Many species of leaf beetle have evolved the ability to run and climb on smooth surfaces and do so using sets of highly specialised adhesive pads. Each leg supports three such pads, which consist of arrays of adhesive hairs (setae) and differ in morphology, both between the sexes and between pads on the same leg. Here we investigate in dock beetles (Gastrophysa viridula) the effect of this variation in seta structure on the mechanical and adhesive properties of the pads. To determine the effective elastic modulus of the arrays, we vertically compressed individual adhesive pads. Distal adhesive pads were significantly softer than middle and proximal ones. Attachment performance was then measured during shear movements and pull-offs from various substrates. Consistent with their greater compliance, distal pads generated higher adhesion and friction on rough substrates. However, the greater stiffness of proximal pads conveyed a superior ability to push. Proximal pads were less direction-dependent than distal pads and generated larger pushing forces in the distal and lateral directions. Locomotion recordings of vertically climbing beetles confirmed that each pad was used differently. When legs above the body centre of gravity were pulling, beetles mainly engaged the distal pads, whereas legs below the body mainly pushed with the proximal pads. We confirmed our findings in flea beetles that have to generate large pushing forces for jumping. While distal pads are used to adhere to smooth substrates, only the proximal pads push when the beetles accelerate for a jump. Our findings demonstrate that there is a division of labour between different adhesive pads on the same tarsus.