Water striders are familiar insects often seen gliding effortlessly across the calm surfaces of ponds, streams, and other freshwater bodies. These slender creatures, sometimes called water skaters or pond skaters, appear to defy gravity as they navigate their aquatic world. Their presence is a common sight, showcasing remarkable adaptations for their unique lifestyle.
How Water Striders Walk on Water
The ability of water striders to walk on water results from two primary factors: the physical properties of water and their specialized anatomy. Water molecules exhibit a strong cohesive attraction, especially at the surface, forming a tightly bound layer. This phenomenon creates surface tension, acting like a delicate, elastic skin. Water striders exploit this natural “skin” for locomotion.
Water striders possess long, slender legs that efficiently distribute their body weight over a wide area on the water’s surface. Each leg is covered with thousands of microscopic, non-wetting hairs that are highly hydrophobic, meaning they repel water. These tiny hairs trap air, which enhances buoyancy and prevents the legs from piercing the water’s surface tension. As the strider moves, its legs create small, temporary dimples on the water without breaking through the surface, allowing them to glide and push off. Their middle legs function like oars, propelling them forward, while the longer hind legs provide stability and aid in steering.
Hunting and Diet
Water striders are predatory insects that primarily consume other small invertebrates that become trapped on the water’s surface. Their diet includes a variety of terrestrial insects like mosquitoes, flies, and ants, as well as aquatic larvae that surface for air. They are adept hunters, relying on their acute senses to locate prey.
The insects detect struggling prey by sensing the ripples and vibrations their movements create on the water’s surface with specialized hairs on their legs. Once a water strider identifies its target, it swiftly moves towards it, using its shorter front legs to grab and hold the victim. The strider then uses its piercing mouthparts to inject salivary enzymes into the prey, which paralyze it and begin to dissolve its internal tissues. The liquefied contents are then sucked out, providing the strider with its meal.
Life Cycle and Habitat
Water striders undergo incomplete metamorphosis, a developmental process involving several distinct stages. Mating occurs on the water’s surface, after which the female lays her eggs. These eggs are often deposited on submerged or floating aquatic vegetation and debris.
After an incubation period, the eggs hatch into nymphs, which are smaller versions of the adult insect. These nymphs progress through several molting stages as they grow into mature adults. Some species can produce multiple generations within a single year. As colder weather approaches, adult water striders often move to sheltered locations on land, such as under leaves or logs near waterways, where they can overwinter until conditions are favorable again in the spring. Water striders are commonly found in freshwater habitats including ponds, marshes, and slow-moving streams, preferring calm water for efficient movement and hunting. A few species, notably those in the genus Halobates, have adapted to live on the open ocean.
Interaction with Humans and Other Animals
Water striders occupy a specific niche in aquatic ecosystems, serving as both predators and prey. Their natural predators include various species of fish, birds, and larger aquatic insects like dragonfly nymphs. Frogs also occasionally prey on water striders.
Regarding human interaction, water striders are not aggressive. They are not known to bite humans in North America, though some larger Asian species have been reported to deliver a painful defensive bite if handled or trapped. Such bites, while rare, can cause localized discomfort. Their primary focus remains on hunting small insects on the water’s surface, and they pose no significant threat to people.