J.H. Crabtree, British Insects and How to Identify Them, Londres, The Epworth Press, 1923, p. 18.

The larva forthwith constructs a safety-tube of sand, small sticks, grass blades, shells, bits of stone, sealed at one end and open at the other. It firmly holds to the lower end of the tube by two hooked appendages. At the approach of danger, the larva instantly withdraws to the tube, and is quite safe from attack.