Cohesion of water molecules is responsible for creating water's surface tension, which allows insects to walk along the top surface of the water, mate and feed on the water's surface. The cohesive property of water is also partially responsible for plants' ability to pull water upward from the roots to the leaves.
Water has two unique properties, cohesion and adhesion, that work together to make water a vital and useful substance for many life processes. Cohesion is the ability of water molecules to stick to one another, and adhesion is the ability of water molecules to stick to molecules of other substances. These forces act together to allow water to flow upward through plants' vascular system. As water evaporates from the surface of the leaves, water molecules that are cohered to the evaporating molecules move upward. The water stays in a tubular shape because it is adhered to the molecules lining the plant's vascular tube.
Cohesion of water molecules is also responsible for surface tension. The water molecules are "stuck together" and resist separating when a small amount of pressure, such as that of an insect leg, is placed on them. As a result, insects and other tiny living creatures can carry out life functions on top of the water's surface. For some species, this water surface provides a breeding ground and feeding place.