Fig. 2.
Photographic explanation of how the giant water strider (G. gigas) jumps on water, including morphological adaptations on midlegs to capture air during penetration of the water. (A) G. gigas on the water surface. The hindleg’s tibiae and tarsi press the surface downward and create dimples during jumping; (B) The midleg’s femur+tibia+tarsi functional unit moves downward while bending and deforming the surface of water to create a dimple (B1), which eventually starts to break (B2), and each midleg continues to operate as a bending rod-like functional unit pushing down in the water after complete breaking (B3) and creating upward drag force. Air sheath is caught among the long hairs on midleg’s tibia and tarsus (D2, F, and G1) and an additional air bubble surrounds the legs (B3), contributing to the drag force. Finally, the midlegs slide out and leave air bubbles (B4). (C) Stacked frames from a jump, starting with the moment right after surface breaking (0 ms) in A. paludum and G. gigas; in A. paludum, midlegs move upward after breaking (C1), the legs of G. gigas move downward in the water (here up to 16 ms from the moment of breaking the surface); (D) SEM image of midleg tibia of the giant water strider (D2) compared with A. paludum (D1); (E) a frame from a high-speed movie (Movie S1) of the midleg experimentally pushed downward in the water to illustrate the presence of air bubble surrounding the fast-moving leg; (F) midleg tibia in water in static situation: the layer of air sheath captured in the hairs around the leg increases the effective radius of the leg; (G) cross-section of the midleg’s tibia to illustrate the distribution of hairs: relatively shorter hair on A. paludum (G2), and longer hair on G. gigas (G1). In (F) and (G), the white broken line with arrowheads indicates the actual radius of the leg while the black broken line with arrowheads indicates the effective radius that captures air sheath and creates drag force (with additional air bubble caught during leg downward). The radius of leg with hair capturing air sheath is marked as , and the radius of leg with the surrounding air bubble is marked as in the model and in Fig. 5. Photo credits: P. G. Jablonski, J. Ha, W. Kim & S.-i. Lee.