Walking on water

Published 6:15 am Tuesday, September 4, 2018

If you’re around ponds or rivers much you will have no doubt noticed long legged bugs literally walking on water. These are water striders (also called pond skippers), and while aquatic strolling is impressive, they also have a few other out of the ordinary attributes.

At a casual glance, water striders (Aquarius remiges) look like spiders, but are in fact insects. It looks like they only have 4 long legs, but two more short ones are tucked below the head. Their ability to walk on water is partly due to water being in love with itself. Molecules of water are more attracted to themselves than anything else, and cling tenaciously to each other. This makes the water surface act like a sheet of rubber. When a strider sets its leg on the water a dimple-like depression forms around it, but the surface holds together, albeit weakly. The striders legs are very specialized to take advantage of this, having thousands of microscopic hairs scored with tiny grooves. These groves trap air, creating more surface area for the leg to float on the water without breaking the surface tension. This is such an efficient mechanism that the water strider could weigh much more and still remain buoyant.

Striders don’t walk on the water so much as they paddle on it. This is done by the middle pair of legs while the other 4 maintain buoyancy. They can move surprisingly fast, which is necessary to catch other critters to eat. One of their favorite meals I’m glad to say is mosquito larvae, which breath through a snorkel they poke up through the water surface. Striders grab the snorkel and pull the larvae out of the water and suck the body fluid out of them vampire-like. Go striders!

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Another oddity of the water striders is their love life. A male strider will without fanfare climb on the back of the female and attempt to mate with her, but if she’s not in the mood she can deploy a shield (think chastity belt) to stop the action. But the male counters this move by tapping the water’s surface, which could attract aquatic predators. And since the female does not want to be eaten, she is likely to allow mating to take place to get the male off her back (literally). So, sex by blackmail….very romantic.

One other weird think about striders is their ability to change whether or not their offspring will have wings. Wings are necessary to move from one body of water to another. But take a lot of energy to maintain. So if the present habitat the female is in is nice and lush, she can trigger a genetic switch so that the next generation has short wings that are not functional but aren’t in the way of day to day activities. But if the habitat is drying up or overcrowded, a genetic switch can be thrown, and the next generation will have functional long wings, and be able to fly to a better habitat. Pretty sophisticated piece of creation I must say.

Steve Roark is a retired area forester from Tazewell, Tennessee.