Physics of Insects on surface of water

 

The surface of liquid due to cohesive forces of molecules below behaves like a stretched membrane, and this property of the free surface of liquid is called surface tension.

Some insects survive and move effortlessly on the surface of the water. These insects have thin bodies and three sets of legs. The legs have tiny hairs that are hydrophobic. This leads to the repulsion of water and flotation provided by the captured air below tiny water insects makes them stride on the surface of water.

If oil is mixed to water then surface tension changes significantly and due to  oil film clinging to tiny hair insects sink in impure water.

Image Courtesy USGS.gov

For Detailed Reading:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4811005/