Have you ever seen an insect gliding across the top of the water and wondered how it manages to do it? Water polarity allows for some animal species to be able to “walk” on the water surface by creating a thin membrane referred to as surface tension.
Polarity occurs because water molecules are made up of one oxygen and two hydrogen atoms that bond together in a structure that looks like Mickey Mouse (the two hydrogen atoms, the “ears,” bond to the same half of the oxygen atom, the “head”). By forming this structure, there is a slight negative charge associated with the oxygen side of the water molecule and a slight positive charge associated with the hydrogen side. When an individual water molecule comes close to another, they attract to each other due to these slight charges, creating surface tension.
Different species of animals use surface tension and special adaptations to be able to “walk” on the water’s surface. Water striders are an iconic species that many people have witnessed walking on water. These insects have long legs with thousands of water-repellent hairs that help distribute their weight and keep them on top of the water. Fishing spiders use hair-covered legs to walk along the top of the water similar to a strider; however, with two additional legs, they can gain enough momentum and surface area to bounce quickly after prey. Some aquatic snails also “walk” on water, but they do so on the underside of the surface. These snails use their foot to create minute waves on the underside of the water surface and adhere mucus to the extra surface area.
While exploring the Great Lakes Bay Region, look closely at water for organisms that are taking advantage of surface tension. Walk by ponds, lakes, marshes, rivers or streams and look for the ripples of animals disturbing the water surface in pursuit of food, travel or air.
Breaking the Water Surface
Many species of animals have adapted to use the water surface in different ways.