Water striders and the surface tension of water
In the pools on both sides of the bridge water striders skate on the surface of the water. These long-legged insects are able to walk on the surface of the water because water has a very high surface tension. Surface tension is caused by cohesion of water molecules to one another by hydrogen bonds. (Water has the highest cohesive force of any liquid except that of mercury). At the air-water interface, the water molecules are H-bonded to one another and to the water molecules below the surface. This makes the water behave as though it were coated with an invisible film. So long as the weight of the insect is not great enough to break the cohesive forces among water molecules, the insect can walk on the surface.
Water striders feed on aquatic insects that come to the surface and terrestrial insects and other organic debris that fall on the surface of the water. They can sense their prey by slight vibrations on the surface of the water.
When food is scarce, they are known to be cannibalistic.
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