Protected by the armour

Frederick George ShawThe Science of Dry Fly Fishing, Londres,  Bradbury, Agnew & Co., 1906, p.66.

The one class, after leaving its eggs, spins a cylindrical case for its future home, to which it attaches small stones, sand, wood, etc.; these cover and mask this case, form an armour-like protection against ennemies, and at the same time act as ballast. The larva uses this tube as a movable residence, and from the open end  its head, thorax, and legs protrude and provide the motive power, the weak and magot-like body being always enclosed and  protected by the armour-clad case which it drags about from place to place.