Tom Anderson, Learning Nature by a Country Road, Stillwater (Minnesota), Voyageur Press, 1989, p. 141.

With my dripping face barely off the water, I may spot a mass of glued-together pebbles and sand grains, resembling an underwater cocoon, crawling along the bottom. Uper closer inspection, I may see tiny insect legs sticking out at one end of the stone work, This is a larval home of one of the many caddis flies. Unable to swim, the larvae slowly crawl along the bottom carrying their protective housing.