24
July 2018
Valley Voice
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‘Boat Almanac
Can You Walk on Water? By Karen Vail
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Water Strider (Heteroptera; Gerridae) Do YOU have a yearning to walk on water? You need to get small. Really small. The size of a water strider small. This enlightenment came alongside the Yampa River while being enchanted by these graceful ballerinas of the water surface. It is interesting that people who have a total bug phobia are mesmerized by water striders. Maybe because they are so easy to observe; even kids excel at it. Maybe because their extraordinary talent on the surface of the water earned them the name Jesus bug (they are also called pond skimmers and water skippers). There have been around 1,700 species of water strider identified; in Colorado 12 species are listed (“Guide to Colorado Insects” Cranshaw, Kondratieff, c2006). They have long, skinny bodies, short front legs used to grasp prey, with two very long pairs of back legs. These back legs are their secret to water skimming (more on that in a bit). They might look like a spider, but they are actually a true bug (really, there is a classification of true bugs!) in the Family Gerridae. And their habitat is water, pure and simple. Lakes, ponds, the quiet edges of streams, puddles, the ocean (the ocean water striders are some pretty amazing bugs!) Back to those legs. Head down to your local water source and watch a water strider moving across the water. They move in a very fluid and graceful way, and wherever their feet touch is a dimple on the water surface. And they are fast!! They can dash after prey at speeds of a hundred body lengths per second (that would be comparable to a six foot tall person swimming at 400 miles per hour!!). (“Hairy Legs Help Bugs Walk on Water” National Geographic News, November 3, 2004, Brian Handwerk) If you just happen to have a microscope to examine those legs and feet, you would see thousands of microscopic hairs. Researchers in China first wrote about these unique hairs less than two-thousandths of an inch and scored by miniature grooves. The grooves trap air, increasing water resistance of the water strider’s legs and improving their buoyancy. The researchers found that the water resistant legs are so buoyant they can support fifteen times the
For those who live here and for those who wish they did.
insect’s weight without sinking (“Hairy Legs Help Bugs Walk on Water”). It’s almost like they have a cushion of air to help them float and move on the water surface, and that air pocket is super hydrophobic (water repelling). Other animals have developed features similar to the water striders’ water repellency, such as duck feathers, but are less effective. If a raindrop lands nearby or a tiny wave swamps them, their buoyancy keeps them from breaking the water surface. If, by rare chance, their legs go underwater, it is very difficult for them to push to the surface. Their weight pushing down on the water causes the surface to deform, hence a dimple under each foot. The graceful movement comes from the middle and hind legs. The middle legs act like paddles, and the back legs can provide some thrust, but are mostly for steering and braking. The front legs, as mentioned earlier, are for snatching prey off the water’s surface. Have you noticed how mosquito larvae hang out at the surface breathing through their little snorkels? Zzzooom, along comes a water strider to snatch that little bugger out of the water with its front legs, pierce the larvae with its needle-like mouthparts, squirt in digestive enzymes that pre-digest the meal then suck out the juices. Go thank a water strider today! It is also the creatures that can’t walk on water that become water strider prey. Hapless moths and crickets flailing about in the water send ripples to the vigilant bugs. They “hear” by feeling vibrations in the water’s surface. Water striders usually wait at the stream’s edge until they hear the dinner bell ring (a vibration of a struggling insect, for example), then dart out to collect their meal. Look up “This is Why Water Striders Make Terrible Lifeguards” (A BBC video from the Deep Look series) video on YouTube for some amazing footage of water strider action. So far water striders seem pretty incredible, but there is one thing that, to me, seems a little weird. As Matthew Miller put it in his blog “7 Cool Facts About Water Striders” (Cool Green Science, Nature Conservancy, April 10,