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A week or two ago, I stood at the bank of a stream watching a group of water striders doing their seemingly physics-defying dance upon the water's surface. So, I decided to try to take some photos, which turns out to be more difficult than you might think (FIRST PHOTO).
Let's dig into two questions:
- What the heck is a water strider, anyway?
- How can water striders run around on the water's surface?
Sometimes called water skeeters, water scooters, or pond skaters, among other names, these insects make up the Gerridae family, in the order Hemiptera (the "true bugs"). Water striders are predators—they feed on mosquito larvae and any other tiny insects that get trapped on the water surface. To help them locate the exact location of their prey, their legs can sense the tiniest ripples in the water. Once they find their prey, they jab the creature with their straw-like mouthparts, inject digestive enzymes to liquify the creature's insides, then suck out the goodies. Cool, huh? (SECOND PHOTO)
So, how do these awesome insects run around on top of the water? First, we have to understand the concept of surface tension. Basically, the molecules in a liquid (including water) have a strange property—they pull on each other in every direction. But at the liquid's surface, the molecules can only be pulled inward by those beneath the surface. This forces the top layer of molecules to tighten up like a stretched sheet of elastic. This is why a glob of water floating in zero gravity forms a sphere, with the least amount of surface area possible. Kind of like a balloon.
And this also makes it so the surface layer can hold a small amount of weight (like a water strider). To make this work even better, a water strider's legs have countless little wax-covered hairs, trapping a layer of air to repel water.
These creatures are magnificently adapted to living and hunting on top of the water. Their short front legs are for catching and holding prey, their long middle legs work like oars to propel them, and they use their long hind legs to steer.
Amazing little boat critters.
What about you? Have you seen any other aquatic creatures that surprise you?
Photo Credits:
- Three water striders - Stan C. Smith
- Water strider close-up - Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons