Monday, August 19, 2013
Amazing Water Skates
When I was a small boy, my parents would occasionally take me to a resort area of the Russian River, known as Cazadero. There were a number of small river beaches just off the highway, and a small tributary called Austin Creek, smaller than the Russian, which was slower and shallower and easy for wading and water play. One in particular access was in a wooded ravine, very idyllic, where we went a couple of times. There was hardly enough water to swim in, just to wade in, really, and there were small semi-stagnant backwater ponds filled with tadpoles and an insect which I found entirely fascinating, though frustratingly elusive. As I came to learn, it lived up to its name: Water Skate. But it had other names, all more or less tied to its amazing ability to skim over the surface of still water: Water Strider, Skimmer, Water Skooter or Skeeter, Water Spiders, etc.
When I first noticed these bugs, I wasn't sure what they were. They looked like insects, but they had a very flat dark grey body without much definition; what I noticed immediately was that they could flash across the surface of the water like lightning! I remember trying to approach them in very shallow pond water, in shade, but whenever I got close enough they'd zip away just out of my reach. They could move a yard or two in a fraction of a second, but they seemed entirely dry, as if they were floating. And yet, as I watched closely, their bodies didn't touch the water. The only parts of their bodies that touched the water were the ends of their legs, which were pointed, like long slim little twigs.
I'm not sure why I thought of these bugs today, but I decided to check out the Wikipedia entry for them, and learned a lot. These bugs belong to the family Gerridae, true bugs in the order of Hemiptera. They have proliferated into a number of species, over 1,700, and are found almost everywhere in fresh watercourses.
I think I probably suspected that there must be something malevolent about these bugs when I first saw them, but they also made me incurably curious. Like most boys, I enjoyed toying with small animals and insects, and these bugs seemed like the perfect toy. Could I catch them? I could not! They were too fast. If I splashed water on them, it didn't seem to affect them. They stayed dry! I wouldn't have understood then about the surface tension of water, which I would learn later in science classes in high school.
Common sense told me, even as a boy, that these bugs should be sinking in the water once they got wet. Wet things, even waterlogged insects, might float, but they wouldn't sit high and dry on the surface. How did they keep from getting wet, and how did they propel themselves across the surface? They only touched the water with the tiny tips of their legs, so why didn't their legs plunge into the water, instead of gliding on the top?
It turns out that these bugs have developed genetically something called Hydrofuge hairs all over their body, and there are several thousand hairs per square millimeter, which allows the bug literally to resist the molecular tension of the water surface. This, combined with a perfect balanced distribution of their body weight along their slender legs, allows them to float. This positioning atop the water surface is called an epipleustonic position, which gives the Water Skater its defining characteristic. The middle set of legs have developed a kind of rowing facility, which allows them to propel their bodies very rapidly across the surface, in large part because of the lack of friction made possible by being "dry" instead of wet. They literally skim across the surface, the way people do on skis over snow, by reducing the friction of the body's weight via the smooth, slippery surface of the ski over compressed snow.
There are a lot of other interesting facts about the Water Skate. They're carnivores, feasting on fallen insects, and can be cannibals as well. Some are born with usable wings, which allows them to fly to other habitat. Others have poor wings but are not subject to getting weighted down with superfluous wings. They can submerge without becoming water-logged, and pop back up.
Apparently they aren't harmful to humans or animals, though they carry certain parasites, and fish don't like the taste of them. Birds are their main predators. They're highly adaptive, which is how they have survived the millennia, and which also explains their considerable species variation. For all my intrepid hunting, I was never able to trap one, or even to kill one. It's been years since I thought about this bug, though I may have inadvertently noticed one while fishing over the last decade or so. When I'm fishing, I tend to be preoccupied with the fish, and the sort of bugs the fish seem to be interested in. Since trout don't like to eat Water Skaters, I just may have unconsciously not noticed them lately.