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We can use boats, skis, rafts and other devices to propel ourselves across the water, but at least 1,200 other species can walk on water without aid. The water strider is one of the most common creatures to perform this feat. This half-inch insect, also called a pond skater, water skipper or Jesus bug, is able to use its amazing legs to walk across the water’s surface.
Water striders can do more than just walk on water. They can stand still on water, they can scoot across it, they can even jump on top of it – all without breaking the surface.
Like all insects, water striders have six legs. But their legs are unusual. They are covered in thousands of microscopic grooved hairs that are water-repellent. The grooves trap air, so water striders do not sink. In fact, water striders can support 15 times their weight without breaking the water’s surface tension. Their legs repel water better than duck feathers. (If detergents were to break the surface tension of water, though, a water strider would sink just like you or me.)
Water striders use their two middle (and longest legs) like paddles to propel themselves forward or backward over the water’s surface.
They use their back two legs to steer and to brake (just like a two-person canoe). They use their short front legs to snatch up prey. Each leg has a joint, so a long leg section rests on the water’s surface to help distribute weight much like how snowshoes keep a hiker from sinking into the snow.
Water striders are insect and spider predators. If an insect falls into the water, it creates ripples as it flounders. Water striders sense the ripples and light reflections from them and rush over for dinner. Water striders can have short bursts of speed, up to 100 body lengths per second. (If a human were to move this fast, she would be going 400 miles per hour!) The water strider grasps its prey, piercing the exoskeleton with its needlelike proboscis. Then it injects saliva that containing enzymes to paralyze the prey and dissolve its innards. The strider sucks up the nutritious insect juice, leaving behind only the empty exoskeleton.
Water striders are our friends: They especially like devouring mosquito larvae and do not usually bite humans.
Water striders escape predators by jumping: The surface of the water acts like a trampoline to help water striders bounce away from critters that want to eat them.
Scientists have used high-speed cameras to learn what happens to water striders during a rainstorm. If a raindrop lands near a water strider, the force launches the water strider into the air, as if the strider were standing on a trampoline. If a raindrop lands directly on a water strider, the drop pushes the water strider down, submerging it – though after the disruption the strider swims back to the surface. If a downpour is huge, a water strider can stay submerged for several minutes because it can breathe from a small bubble of air it carries around.
Some water striders communicate by making ripples with different frequencies. A fast ripple (25 Hz) is a repel signal. A short ripple (3 Hz) is a courtship signal. When a male water strider spies another, it sends out a repel signal; if the other water strider does not respond, the male knows he has spotted a female – and sends out a courtship signal. If the female is not receptive, she sends back a repel signal. If she sends no signal, she is receptive, and the male water strider approaches. After mating, the female attaches her fertilized eggs to plants or stones, with the number of eggs she lays depending on how much food she’s eaten in previous weeks. The eggs hatch in a couple of weeks.
Water striders are true bugs. Their young, called nymphs, look just like wingless adults, only smaller. They go through five molts, shedding their exoskeleton each time as they grow into adulthood. This process takes about two months.
Water striders have claws on their front legs for capturing prey – but not at the as you might expect. The claws are further up the leg so they do not pierce the water and destroy its surface tension, sinking into the water instead of briskly skating.
Water striders sense and adapt to the changing environment: A female may produce one brood with short or nonexistent wings, followed by a second brood with large wings that allow them to fly to nearby bodies of water when their current pond is too crowded or in danger of drying up. Short or nonexistent wings, on the other hand, allow a water strider to dedicate its energy to earlier reproduction and producing greater numbers of eggs. Water striders that overwinter have wings so they can fly to water in the spring.
These insects overwinter as adults. As days become shorter, their bodies store fat to live on during their winter dormancy. They bury themselves under leaf litter or under rocks or logs to ride out the winter. In the spring, they fly away, looking for a lush body of water.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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