We frequently observe

« Natural Science », The Herald of Truth, a Monthly Periodical devoted to the Religion, Philosophy, Literature, Science and Art, Cincinnati, L.A. Company, juillet, vol. II, 1847, p. 13-14.

The general name of the perfect insects is Phryganea ; and the larvae are know from their habit of forming cases of extraneous bodies, in which they enclose and protect themmselves. We frequently observe, in pools, bits of straw, as it were, moving as the bottom ; there are the cases of the caddis larvae. The inner side of the cases is lined with a substance like silk, composed of threads which the larvae spin. For defense, there is attached to the silken wall an outer battery, either of stone work, composed of bits of gravel, or pieces of wood, or grass, or dead straws, &c. ; there being as many varieties of the case as there are species of the insect. It will be seen, on studying this among the most insignificant of living things, that it is not without interest ; for its operations are governed by an inscrutable wisdom. The caddis worm is specifically heavier than water, and, consequently, in constructing its case, it is of the utmost importance that it be made neither too light, nor too heavy ; if the former, it would float ; if the latter, it would be troublesome and inconvenient for the animal to drag along. It has the skilll therefore, to form the case of the exact buoyancy necessary : should it be too heavy, it attaches a piece of straw, wood, or other light substance, to give the requisite levity ; and if too light, it gives the due quantum of ballast by glueing on a stone or shell.