The case is dragged behind

Bernard VenablesFreshwater Fishing, Ill Bernard Venables  Londres  Panther Book, 1969, p. 135.

They live in cases of their construction, tubes made of pieces of grit, pieces of stick, pieces of weed, the mode of construction varying with the species. When the insect moves in its particular environment- in theweeds or on the bottom- its forepart, which is dark brown, emerges from the case so that the legs can be used. The case is dragged behind. The abdomen, which remains in the case, is dirty white.