Question

On an atomistic level – why can pond skaters and other small creatures walk on water, whereas we can’t? Similarly, why is it that mosquitos can’t breed in pondwater that has had a small amount of kerosene poured onto it?

Answer 1

The answer to the first part of the question:

Pond skaters and other small creatures that can walk on water use their small weight and the surface tension of water to stay afloat on the water surface which we can't do as we are a lot heavier than what the surface tension of water can sustain. It has been found from studies that creatures like pond skaters have hair on their legs and the hair is covered by a waxy substance that allows bubbles to be attached to them to keep the water out when the hair penetrates the water surface. The hair on the middle one of the 3 pairs of legs that insects have is used by them to create vortices to move across the water.

The answer to the second part of the question:

Kerosene or any other kind of oil usually has a specific gravity less than the water due to which it forms a film over the water surface blocking the transfer of oxygen from the atmosphere to the pond water. Since oxygen is necessary for breeding, insufficient supply of oxygen kills the larvae of the mosquitos and thus stops them from breeding in the pond water.