Page:Popular Science Monthly Volume 41.djvu/186

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174
THE POPULAR SCIENCE MONTHLY.

what and where to seek, often find this moth, either singly or in pairs, resting with folded wings within the half-closed flowers. It is then not only hidden from ordinary view, but well protected by the imitative color of the front wings with that of the flower, so that close scrutiny is necessary for its detection. If we visit the plant after

"... the garish day
Has sped on his wheels of light away,"

and when, with full-blown perianth, the yucca stands in all her queenly beauty, and sends forth her perfume more strongly upon the night air, we shall, with a little patience, meet with this same moth, flitting swiftly from flower to flower and from plant to PSM V41 D186 Generic characters of pronuba yuccasella.jpgFig. 3.—Generic Characters of Pronuba yuccasella: a, side-view of head and neck of female denuded, showing how the collected load of pollen (1) is held by the tentacles (2); b, maxillary tentacle and palpus; c, an enlarged spine; d, palpus separated; e, scale from front wing; f, front leg; g, labial palpus; h, i, front and hind wings denuded; j, anal joint of female with ovipositor—all enlarged. plant—the dusky nature of the hind wings and of the under surface of the front wings almost completely offsetting and neutralizing, when in motion, the upper silvery whiteness of the latter, and thus still rendering the insect a little difficult of detection. It is principally the male which we thus see flying and, by the aid of a "bull's-eye," we shall find the female for the most part busily at work in the flowers. He, with relatively stronger wing-power, can afford to spend in the most pleasurable way the few brief days allotted to him; but she is charged with a double duty, and loses little time in its performance. As a part of the maternal task of continuing her race, she must act as foster-mother to the plant in order to insure a proper supply of food to her larvæ, which, as we shall presently see, feed on its seeds.

As preliminary to a better understanding of the habits of the female, it will be well to draw attention to those structural peculiarities which distinguish her from all other species of her order, and which so admirably fit her for the work she has to do. Fig. 3 gives some details of the head (a), and an important structure which more particularly characterizes her and interests us is the maxillary tentacle, shown with its palpus at b. She has a pair of these organs, which are prehensile and spinous, and it is chiefly by means of these that she is able to collect and hold a relatively