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Spring 2010

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

water strider casts shadows

A water strider skates across a stream, its legs pressing dimples into the surface, which cast shadows on the streambed.

May 4, 2010

Water striders, leg lenses

In sunny shallow streams, the shadows cast by water striders are easier to see than the animals themselves.

Also known as pond skaters or water skippers, the insects patrol the water's surface, preying upon any small invertebrate that they can capture with their forelegs and pierce with their sucking mouthparts.

Their legs are covered with microscopic water-repellent hairs, which allow the striders to scamper across the surface of the water, using forelegs and hind legs for steering and middle legs for rowing.

As though they were pressing down on a trampoline, each of the six legs distorts the water's surface tension, bowing the water down to create a concave lens that sends light waves into a bright ring and creates a dark lens shadow inside the ring.

water strider lens

SOURCE: Wayne H. Knox, Institute of Optics, University of Rochester