EPOW - Ecology Picture of the Week

Explanation:   Water Striders are common denizens of ponds and slack water areas of streams, such as this pool in a northwestern California stream.  They are masters of walking on water, using not buoyancy but surface tension to whisk across the slick surface.  

The 3 images in the above animation illustrate how they bend the surface of the water to get their foothold. 

The first image shows the body and legs of the insect on the surface.  

The second image shows how light refracts around the curved water surface under each leg, almost like lines of force around a magnet.  

And the third image shows the shadow of the refracted light on the bottom of the stream, illustrating the extent to which each leg causes a depression in the water surface.  

(This unique three "dimensional" image was created from 3 digital telephotographs.)

Actually, use of robots have helped show that water striders glide across the water surface with a combination of rowing and using water tension friction.  

What can disrupt the surface tension?  Pollutants from household detergents can break the molecular surface tension, rendering it difficult to impossible for the strider to, well, stride.  

New information:  Wotton, R. S., and T. M. Preston. 2005. Surface films: areas of water bodies that are often overlooked. BioScience 55(2):137-146.