The Integument of Water-walking Arthropods: Form and Function John W.M. Bush a , David L. Hu b and Manu Prakash c a Department of Mathematics, MIT, Cambridge, MA, USA b The Courant Institute of Mathematical Sciences, NYU, New York, NY, USA c Center for Bits and Atoms, MIT, Cambridge, MA, USA 1 Introduction 118 2 Surface tension 120 2.1 Weight support 124 2.2 Capillary attraction 128 2.3 Propulsion 130 3 Wetting 131 3.1 The contact angle 132 3.2 Surface roughening 133 3.3 Contact angle hysteresis 139 3.4 Water-repellency 142 4 Insect cuticle 144 4.1 Composition 144 4.2 Morphology 145 4.3 Stability 153 5 Function 157 5.1 Water- and rain-proofing 157 5.2 Plastron respiration 161 5.3 Clasping the free surface 165 5.4 Drag reduction and thrust generation 167 6 Imaging techniques 169 6.1 Scanning electron microscopy 170 6.2 Optical microscopy 173 6.3 Scanning probe microscopy 176 7 Discussion 177 Acknowledgements 181 References 181 ADVANCES IN INSECT PHYSIOLOGY VOL. 34 ISBN 978-0-12-373714-4 DOI: 10.1016/S0065-2806(07)34003-4 Copyright r 2008 by Elsevier Ltd All rights of reproduction in any form reserved