How insects move over water ?
Insects move over water surface not due to Archemidus principle but due to surface tension of water.
The insects and leaves float over water surface due to surface tension of water
All the liquids have surface tension due to which surface of liquids is stretched and small insects, leaves and razer blades can float over the surface.
Archimedes principle do not apply in this case because objects are completely on the surface and are not partially or completely submerged in the liquid. Moreover if some detergents like soap is applied on the surface the razer blade sinks because surface tension decreases if detergents are applied.
Origin of surface tension:
The origin of surface tension is cohesive force. The molecules of liquid attract each other.Inside the liquid every molecule is attracted to all sides because it is surrounded by other molecules from all sides but surface molecules are attracted only from downward molecules because there are no molecules above them so surface of liquid is stretched downward which we call surface tension.