Water Striders Don't Stride. They Row Across the Surface of the Water
Posted on August 31, 2011
Water striders are insects known for their ability to travel across the surface of the water in a pond or creek. MIT researchers have discovered that water striders do not actually stride across the water. What striders do to move about in the water is more like paddling or rowing.
National Geographic reports that the insects press down on the surface of the water with their skinny legs. This creates dimples in the water around their feet. The water striders then propel themselves forward by using these dimples like the blades on an oar.
In a release the MIT researchers say newly hatched water striders can row just as well as adults.
As the insect rests on the surface, the tips of its thin legs create miniscule valleys. It sculls the middle set of its three pairs of legs like oars, causing the water behind those legs to propel it forward as the surface of the valley rebounds like a trampoline.MIT graduate students David Hu and Brian Chancreated a robotic strider, called robostrider, to mimic what the water striders do in the water. Robostrider and a water strider are seen together in the photo above.Although the rowing motion does create tiny waves, "the waves do not play a significant role in the momentum transfer necessary for propulsion," the researchers wrote. "The momentum transfer is primarily in the form of subsurface vortices."
The MIT researchers also put food coloring in a tank to show how water striders generate vortices in the water. Science Friday interviewed David Hu about the water striders' unique rowing ability. Take a look: