a, An adult water strider Gerris remigis. b, The static strider on the free surface, distortion of which generates the curvature force per unit leg length 2 sin that supports the strider's weight. c, An adult water strider facing its mechanical counterpart. Robostrider is 9 cm long, weighs 0.35 g, and has proportions consistent with those of its natural counterpart. Its legs, composed of 0.2-mm gauge stainless steel wire, are hydrophobic and its body was fashioned from lightweight aluminium. Robostrider is powered by an elastic thread (spring constant 310 dynes cm^-1) running the length of its body and coupled to its driving legs through a pulley. The resulting force per unit length along the driving legs is 55 dynes cm^-1. Scale bars, 1 cm. Copyright: Nature (http://www.nature.com/nature/journal/v424/n6949/fig_tab/nature01793_F1.html).

Images captured from a side view indicate their hemispherical form. a, A thin layer (2−5 mm) of thymol blue was established on the surface of the water, disturbance of which revealed the vortical footprints of the water strider. b, The ambient texture results from Marangoni convection³⁰ in the suspending fluid prompted by thymol blue on its surface. The starburst pattern results from the chunk of thymol blue evident at its centre reducing the local surface tension, thus driving surface divergence that sweeps away the dyed surface layer. The fluid is illuminated from below; consequently, the light-seeking water strider is drawn to the starbursts. Scale bars, 1 cm. Copyright: Nature( http://www.nature.com/nature/journal/v424/n6949/fig_tab/nature01793_F4.html).

Green sea-turtles, Chelonia mydas, are able to navigate accurately across vast distances. Copyright: Nature (http://www.nature.com/nature/journal/v428/n6986/fig_tab/428909a_F1.html ).

Turtle with attached permanent magnets.Copyright: Universita di Pisa (http://www.deee.unipi.it/islameta/Research/Sea%20Turtle%20Navigation/Magnet%20photo.jpg).