Found in freshwater ponds and still bodies of waters, the water strider, or pond skater, is a predatory aquatic insect that uses the highly sensitive water-repellent hairs on its legs to detect the vibrations of an insect as it falls into the pond. The strider will then race to the location to nab its prey. Despite being denser than water, a water strider doesn’t sink; instead it exploits the principle of water tension to stay on the surface.
The forces of attraction between all the molecules in the water pull the molecules at the surface together so that they lock like a thin elastic membrane of slightly denser molecules. The water strider can then cross the surface without sinking.
Water striders have three pairs of legs, the front pair of which are short and dextrous enough to clasp, kill and eat small prey. The middle pair of legs, lying flat on the water, are used as oars to ‘row’ over the surface while the rear pair act like rudders for steering. Long, splayed legs enable the pond skater to distribute its weight evenly over a greater surface area, further helping it to float.