Secret of walking on water uncovered
 Insects use legs to create vortices in water

  If you have ever wondered how insects like water striders walk on water or skim across the surface of ponds, rivers and oceans, scientists at MITref  have the answer. Rather than move by creating waves, as some researchers had thought, the insects use one of their three sets of hairy legs like oars to create vortices or spirals in the water that propel them forward at speeds of up to 150 cm (60 inches) per second.
 
Figure legend: A water strider leaves a trail of whirling water in its path. A blue chemical was sprinkled on the surface of
the water and special illumination from below was used to highlight the convection pattern created by the strider's walk.
 
     John Bush and colleagues at the Massachusetts Institute of Technology, who discovered the secret said that although tiny waves were created, they were not the main driving force.  “The momentum transfer is primarily in the form of subsurface vortices,” Bush said in a report in the science journal Nature.

     Water striders, also known as skimmers, come in hundreds of different species ranging in size from one centimeter (about half an inch) to the giant Vietnamese variety — 20 times bigger and still able to walk on water.The researchers discovered the secret by using sophisticated tracking and a high-speed video camera that showed the curlicue patterns they made 9see figure above).
     They also created a mechanical water strider, called Robostrider, based on the real thing. It is made out of a drinks can, with stainless steel wire legs and an elastic band and pulley as its middle legs.
 

     The "Robostrider" facing a real water strider.
 
reference 1:   The hydrodynamics of water strider locomotion, by David L. Hu, Brian Chan & John W. M.
     Bush - Nature 424, 663–666 (2003); doi:10.1038/nature01793
reference 2:   Animal locomotion: How to walk on water.  How the short legs of juvenile water striders
     propel the insects across water has perplexed researchers. It now appears that walking on water shares
     features with the locomotion of birds, insects and fish.  by Miachael Dickinson - Nature 424, 621–622
     (2003); doi:10.1038/424621a