Meeting Abstract

P3.37  Tuesday, Jan. 6  Soft dynamics — ground reaction forces in a crawling caterpillar LIN, H.*; TRIMMER, B.A.; Tufts University; Tufts University huai-ti.lin@tufts.edu

Most terrestrial soft bodied animals move by pressing against the substrate in carefully controlled sequences. However, lepidopteran larvae have well-developed limbs (the prolegs) that can be used for climbing in complex branched structures and on a variety of surfaces. The tobacco hornworm, Manduca sexta is therefore an excellent animal to study how limbed locomotion in soft-bodied animals compares to that of legged animals with rigid skeletons. In this study, we devised a method to measure the ground reaction forces (GRFs) in fifth instar Manduca at all contact points during crawling. A multi-sensor array was built to match the step pattern of the caterpillar and to measure the GRF exerted by each proleg with <mN accuracy. By tracking individual proleg movements a GRF profile could be determined for each segment. During horizontal crawling different prolegs were found to have their own characteristic ground contact pattern with stereotypic crochet protraction. Remarkably, the crochets release their grip with negligible upward force. Simultaneous measurement of all proleg GRFs normal to the direction of travel revealed a rhythmic redistribution of body weight corresponding to the ground thrust during stepping. The work done by different prolegs could be estimated by following the moving center of mass and, by integrating the GRF data, we were able to deduce the effective momentum during various phases of locomotion. Similarly, from GRF loading rates, we obtained invaluable information about force propagation. These findings could help to understand how soft-bodied animals exploit internal dynamics to exert forces on their environment.