On our last program, we learned how water bugs manage to stand on the surface of a pond: The pads of their feet resist contact with the water just like wax paper does.
This allows the bug to rest on the thin film of surface tension that naturally covers the pond. This surface tension film is caused by the strong attraction the surface water molecules have toward each other, as well as toward the water beneath them.
Staring To Move…
While this is fine for standing on water, you might wonder how a water bug actually starts moving.
After all, there’s virtually no contact between the bug’s feet and the water, so there’s no friction for the bug to push against. It would be like wearing slippery shoes on flat, wet ice–you might slide your feet around, but you couldn’t get anywhere.
How Do Water Bugs Move?
The answer lies in the little dimples that a water bug’s feet make in the otherwise flat surface. If the water’s surface really stayed as flat as ice, the bug wouldn’t be able to move. Those dimples give it some grip.
Here’s how it works: The back side of each dimple provides an angle for the bug’s leg to push against. Even though the bug’s push makes the dimple move slightly backwards in the water, there’s still enough purchase for the bug to push itself forward.
It’s like jogging through soft, dry sand. Our feet push the sand backward, which makes running a lot harder, but we can still move forward.