Nature on our doorsteps: The ability of walking on water

By Rosaleen Dwyer

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures

The ability to walk on water is a skill that insects like Pond Skaters have. 

These insects live on the surface of ponds and slow-moving water, feeding upon the many other insects that drop onto the water.

Pond Skaters bend the surface of the water compressor

Pond Skaters 'bend' the surface of the water

Small insects and spiders can walk on water only when their weight is light enough to be supported by a natural force called surface tension. 

Underneath the water’s surface, water molecules bond closely together. 

At the surface however, because there are no water molecules above them to bond with, the water molecules in this surface layer cling even more tightly to one another. 

This extra strong bond at the surface causes a thin film of tension to form. This film can be strong enough to hold the weight of small insects and spiders.

As these creatures move around, their feet ‘bend’ the water but they don’t break the surface bond, moving around as if they were on a gently bouncing trampoline.

Pond Skaters will sometimes catch very young tadpoles if they come too close to the surface compressor

Pond Skaters will sometimes catch very young tadpoles if they come too close to the surface

The legs of these surface dwellers are usually placed far apart, spreading their weight safely over a larger area. 

Their feet also have tiny hairs that trap air, keeping them dry.  If their feet got wet, this would break the surface tension and cause them to sink into the water.

Clearly, there is a lot of physics involved for Pond Skaters living in such a specialised habitat!

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