Ralph Cutter, Fish Food, A Fly Fisher’s Guide to Bugs and Bait, Ill. Lysa Cutter, Mechanicsburg (PA), Stackpole Books, 2006, p. 83-84. 

They find the perfect piece of material and chew it down to the perfect size. In some creeks, pine needles are the building material of choice ; in others, it might be lodgepole bark ; and in still other waters, it might be strips of sedge. Regardless of what the material is, the Brachycentrus build a perfect home.

Their cases are shaped like chimneys that are slightly narrower at the base than at the mouth.The corners are mated to create impeccable right angles, and the square profile is clean and neat. With all the power tools in the world, I certainly couldn’t make anything so flawless, so how can a damn insect do it with only its teeth ?