Anonyme, Dialogues on Entomology in Which the Forms and Habits of Insects are Familiary Explained,Londres, Printed for R. Hunter, 1819, p. 185-186.

Mother: The genus I shall first mention to-day is called phryganea, or vulgarly, spring fly.During its larva state it lives in the water ; its shape is that of a long worm with six legs ; and it spins about itself a silken tube, wide enough to turn round in, so that it can put out its head at the aperture in either end.

Lucy: The silken case must be so light, that perhaps the worm can swim about with its house on its back ?

Mother: It is indeed so light, that the little creature cannot without some contrivance sink itself to the bottom of the water, in search of its prey. For this purpose it glues to the outside of the case, grains of sand, gravel, or small shells, which  in creases its specific gravity, or weight, and enables it to dive ; if it happens to have glued on so many as to make its house too heavy to float, the nit sticks on, in addition, bits of straw, or rotten wood, or grass ; thus endeavouring to keep itself exactly suspended in the water ; by whichmeans it can both run, and swim, and sink with equal ease.