Moving along without cause

F. G. Sanborn, « Essay on some of the insect of Massachusetts which are beneficial to vegetation »,Report of the Secretary of the Massachusetts Board of Agriculture, Government Printing Office, 1863, p. 162-163

The family Phryganina, (from Phryganon, a dead stick or faggot,) was so named by Linnaeus, in allusion to the habits of the larvae which construct a tube of sticks, or other substances, as a protection against their enemies. Being a whitish, plump grub, and slow in its motions the larva would form a delicate morsel  for fish, or voracious aquatic insects of different species, were it not endowed with sufficient instinct to build a shelter for its existence in this state, and its succeeding transformations. In the bottom of almost every pool, or brook a curious structure composed of pieces of bark, dead twigs, grains of sand, sometimes a bright green leaf, or even small shells, may be seen, apparently moving along without cause but closer examination will discover a small, brownish head, and six legs, at one end, which are quickly retracted on being touched.