Optics at the creek

At the bottom of a canyon, the clear, cold waters of a creek make their way noiselessly to the Pacific. The heat of the warm spring day hasn't yet reached through the canopy of big-leaf maple trees. Over the surface of the stream, a tiny gnat that didn't stretch properly before flight pulls a wing muscle and shortly thereafter tumbles into a sunlit patch of water. Because live gnats don't sink, but do have some parts that "wet" with water, the gnat becomes trapped on the water surface and can't fly off. A water strider, Gerris lacustris, senses the ripples generated by the struggling insect, skates over, and has lunch.

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