Meeting Abstract

88.4  Sunday, Jan. 6  Jumping without slipping: spiders need sticky feet for take-off GOETZKE, H.H.*; FEDERLE, W.; University of Cambridge; University of Cambridge hhg24@cam.ac.uk

Many insects and spiders can perform rapid jumps from smooth plant surfaces. If jumping arthropods relied only on classic friction, they should slip on smooth surfaces except for very steep take-offs. They can only overcome this biomechanical problem by using surface adhesion while accelerating. Most adhesive structures only grip when pulled toward the body, but jumping with hind legs requires pushing, against the usual direction-dependence. We studied how jumping spiders (Pseudeuophrys lanigera and Sitticus pubescens) leap from smooth surfaces. Both species accelerated with their 3rd and 4th leg pairs. In P. lanigera the jump was mainly powered by the 3rd legs, and 4th legs touched the surface only at the start of the jump. In contrast, S. pubescens mainly used the 4th legs while the shorter 3rd legs detached early. The different position of the leg pairs in both spiders resulted in a different orientation of the tarsus during take-off. While 4th-leg tips pointed backward in both species and pushed, 3rd-leg foot tips in P. lanigera were oriented forward and pulled. This opposite tarsus orientation led to the use of different attachment structures. High-speed video microscopy recordings of tarsi during take-off revealed that “pulling” 3rd legs in P. lanigera made brief (~9 ms) adhesive contact with their claw tuft setae. In contrast, the distal claw tuft setae of “pushing” 4th legs were lifted off the ground, and contact was only made by some setae of the proximal pretarsus. In S. pubescens the 3rd legs were oriented laterally and adhesive contact was only rarely visible, while “pushing” 4th legs made clear adhesive contact with proximal claw tuft setae. Experimental ablation of adhesive structures caused accelerating spiders to slip, confirming that adhesion is essential for jumps from smooth substrates.