Why do certain larvae form an exterior covering or cocoon?
Because the pupa may be lodged with greater safety. This covering is in some composed of threads of silk. Sometimes only one or two threads are required to keep the pupa in a proper position ; in others, the silk is woven into cloth, or so matted together, as to resemble paper. The matter, of which these cases or cocoons are fabricated, is prepared by two long tubes, which take their rise in the abdomen, enlarge as they approach the head, and terminate by a duct, which opens under the labium, or lower lip. By pressing the orifice of this duct to one place, and then to another, the larva draws out the tenaceous threads. – Fleming.
