The water strider, an insect belonging to the family Gerridae, is a common sight on the surface of freshwater bodies across the globe. Characterized by its long, slender body and disproportionately long legs, this insect appears to effortlessly glide across the water without sinking. This unique ability has earned it several common names, including pond skater, water skeeter, and the “Jesus bug.” Water striders are true bugs of the order Hemiptera, with over 1,700 described species.
The Science of Walking on Water
The water strider’s ability to remain suspended relies on the physical property of surface tension. Water molecules are strongly cohesive, forming a taut, membrane-like layer on the surface that resists penetration. The insect’s light weight is distributed across its long legs, which depress this surface film without breaking it, creating small dimples known as menisci.
The legs are covered in thousands of microscopic, water-repellent hairs called microsetae, coated in a waxy substance. These structures trap air and prevent the legs from getting wet, making them highly hydrophobic. This water-repellency ensures the insect’s body and legs push away from water molecules, maximizing surface tension for buoyancy.
Movement is achieved using a specialized tripod gait involving its three pairs of legs, each with a distinct function. The short front pair of legs is held up and used for grasping prey, while the middle and hind legs are dedicated to locomotion. The middle legs act like oars, propelling the insect forward by pushing against the vertical surface of the menisci they create.
The long hind legs provide both steering and additional thrust, ensuring the strider can move quickly and change direction with precision. By pushing backward against the water, the middle legs leverage the restoring force of the water’s elastic surface film to achieve impressive speeds. Some species can dart across the water at a rate equivalent to one hundred body lengths per second.
Diet and Hunting Strategy
Water striders are predatory insects that feed on invertebrates, primarily terrestrial and aquatic insects that fall onto the water’s surface. They also consume larvae and other dying or dead organisms trapped by surface tension, functioning as both active hunters and opportunistic scavengers.
The strider’s primary method for finding food relies on its highly sensitive legs, which detect minute vibrations and ripples on the water. A struggling insect creates distinct ripples that the water strider can pinpoint, accurately determining the location and size of potential prey. This detection system is precise enough to distinguish prey ripples from those caused by wind or other disturbances.
Once the prey is located, the water strider uses its short, strong front legs to quickly grab and hold the victim. It then utilizes its piercing-sucking mouthparts, known as a rostrum, to penetrate the prey’s exoskeleton. Specialized salivary enzymes are injected to liquefy the internal tissues, and the strider draws the nutrient-rich fluid through the rostrum.
Habitat and Distribution
Water striders are found globally, inhabiting most regions of the world with the exception of the extreme polar areas. They thrive in environments where the water is calm and still, allowing surface tension to remain undisturbed. Common habitats include the surfaces of ponds, marshes, lakes, and slow-moving sections of streams and rivers.
Aquatic vegetation is a favored feature of their habitat, providing shelter and a substrate for reproduction. After mating, females typically lay eggs by attaching them to submerged objects like rocks or aquatic plants near the water surface. The life cycle involves incomplete metamorphosis, where the nymphs resemble smaller, wingless versions of the adults.
While the vast majority of species inhabit freshwater, a small number of genera, such as Halobates, have adapted to live in marine environments, making them the only known insects to live on the open ocean. Water striders generally prefer warmer temperatures for activity. In temperate climates, adults often seek shelter in shoreline vegetation to hibernate during the winter months.