Dynamics of prey prehension by chameleons through viscous adhesion

Par Pascal Damman, Laboratoire Interfaces & Fluides Complexes, Université de Mons

Mardi 18 Septembre, 14h00, Salle des séminaires (215), 2ème étage, Bâtiment A4N

Abstract :

Among predators using an adhesive tongue to feed, chameleons are able to capture large preys by projecting the tongue at high acceleration. Once in contact with a prey, the tongue retracts with very large accelerations to bring it to the mouth. A strong adhesion between the tongue tip and the prey is therefore required during the retraction phase to overcome the inertial forces and ensure a successful capture. To investigate the mechanism responsible for this strong bond, the viscosity of the mucus produced at the chameleon’s tongue pad is measured, using the viscous drag exerted on rolling beads by a thin layer of mucus. We show that the viscosity of this secretion is about 400 times larger than that of human saliva. We incorporate this viscosity into a dynamical model for viscous adhesion, which describes the motion of the compliant tongue and the prey during the retraction phase. The evolution of the maximum prey size with respect to the chameleon body length is then derived, and compared with in vivo observations for various chameleon species. Our study shows that the size of the captured prey is not limited by viscous adhesion, owing to the high mucus viscosity and large contact area between the prey and the tongue.