The four long legs that extend outward from the narrow body are supported by the tension of the water surface. The first pair of legs is raptorial; they are used to seize food and hold it while eating. Water striders occasionally eat other small aquatic animals, but mostly they feed on ter- restrial insects such as flies that fall onto the water surface. Water striders have sensory organs on the ends of their legs that can detect slight vibrations and even distinguish among different kinds of prey.