十万个为什么·科学阅读30篇（1）

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为什么有些昆虫能在水面上行走而不破坏水面？

Water striders and other pond skaters stay afloat thanks to surface tension—the skin-like film formed by hydrogen bonds between water molecules.
Their long, thin legs spread weight evenly and are covered with microscopic wax-coated hairs that repel water.
This hydrophobic coating prevents legs from piercing the surface, letting them rest on top like tiny rafts.
Even raindrops hitting nearby create ripples they sense instantly with sensitive leg receptors.
They move by pushing sideways against surface tension, not by paddling downward into the water.
Scientists mimic this design to build micro-robots that clean oil spills on calm water surfaces.
If water is polluted with soap or alcohol, surface tension drops and insects sink immediately.
This ability works best on still ponds—not choppy rivers—because waves disrupt the delicate force balance.
Evolution shaped these legs over millions of years to exploit physics rather than fight it.
Watching them glide reminds us that nature solves problems using forces we often overlook.