Water Striders
This is one of two water striders that I caught on the little stream that runs alongside of our road. They are normally almost impossible to catch, but I spotted a pair that was mating. They were moving pretty slowly, and I was able to corner them up against some rocks and nudge them into my collecting jar. They unfortunately stopped mating by the time I got them home, so I couldn’t get a picture of them both at once.
Water striders are a bit unusual, in that they don’t live exactly in the water, or in the air. Instead, they live on the interface, supported by the surface tension of the water. The tips of their long legs are supported on the surface, with a long, narrow foot to spread out the weight enough that they don’t punch through.
Other than being long, the foot doesn’t have any obvious structure to help the water strider stay afloat. However, the whole insect is highly water-repellent: when I released them, I poured them back into the water, and they bobbed to the surface instantly, still dry as a bone.
Water striders are the family Gerridae, and these are probably in the genus Aquarius. They use the four long legs to skim along, and use their front legs to snatch other small arthropods through the surface of the water
They are true bugs, and have the typical bug-style sucking mouthparts. This one flashed its proboscis so that we can see it properly:
While they are obviously most at home on the water, they can go onto land if they want to. I dropped one onto the kitchen floor, and while it was kind of clumsy, it could move along all right. And, when alarmed, it could jump surprisingly well, clearing up to 5 inches on some jumps.
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Beautiful.
Here’s an article (from Korea) on water striders:
Solving another mystery of an amazing water walker
Journal Information
Journal: Langmuir
Journal Article: “Impact of a Superhydrophobic Sphere onto Water”
Read the article online
Download the PDF
Walking on water may seem like a miracle to humans, but it is a ho-hum for the water strider and scientists who already solved the mystery of that amazing ability. Now researchers in Korea are reporting a long-sought explanation for the water strider’s baffling ability to leap onto a liquid surface without sinking. The study is scheduled for the Dec. 18 issue of ACS’ Langmuir, a bi-weekly journal.
In the new study, Ho-Young Kim and Duck-Gyu Lee note that scientists already have discovered the hydrophobic, or water-repellent, structure of the water strider’s legs and how they allowed the creatures to scoot along ponds and placid lakes. However, their ability to jump onto or “bounce” off liquid surfaces remained a lingering scientific mystery.
Kim and Lee solved it by dropping a highly water-repellent sphere onto the surface of water at different speeds, carefully tracking its motion with high-speed cameras. They found that the ball must be traveling within a narrow velocity range in order to bounce off the water’s surface. The sphere may sink if it goes too fast and won’t bounce back if too slow. “The highly improved ability of heavy hydrophobic solids to keep afloat on water even after impacting upon water with a high velocity appears to explain partially why water striders have superhydrophobic legs,” say the authors. “Application of our study can be extended to developing semi-aquatic robots that mimic such insects having the surprising mobility on water.”
http://pubs.acs.org/cgi-bin/abstract.cgi/langd5/2008/24/i01/abs/la702437c.html
Impact of a Superhydrophobic Sphere onto Water
Duck-Gyu Lee and Ho-Young Kim*
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Korea
Received August 8, 2007
In Final Form: September 19, 2007
Abstract:
When a water drop hits a superhydrophobic solid surface, it bounces off the substrate like an elastic ball. Here we show that when a tiny superhydophobic solid sphere impacts with water, it can bounce off the free surface just as it impacts with an elastic membrane. The motion of a sinking sphere is analytically calculated by solving a potential flow whose free boundary is determined by the Young-Laplace equation. To find conditions under which the solid sphere should sink, bounce off, or oscillate upon impact with water, we construct simple scaling laws which are shown to agree well with experimentally found boundaries between the distinct impact behaviors in a regime map based on dimensionless parameters.
Thank you!!!
I’ve been trying to find any website that could help me on a science paper about water striders.
Thanks dude (or dudette)!!
Just out of curiosity, what is your name
Thanks, I neede this