Marvel of adaptation

Kay DunbarLanscape into Litterature, Cambridge, Green Books, 2005, p. 85.

It sprouts male ferns from its crevices and sometimes, very rarely, I have seen a dipper here – another marvel of adaptation – prising caddis fly larvae from their stony, self-secreted tubes on the bottom of the stream.  What drove the wren to enter the floor? What tweak of selection made it submerge for its super when a million bugs throng the surface of the water?