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The Vice-Reine (Especially interesting feature)
The especially interesting feature of this group is found in the caterpillar habits.
The egg is laid on the tip of the leaf of the food-plant and as soon as the little caterpillar hatches it begins feeding across the end of the leaf, leaving the midrib. It feeds only by night, and during the day rests stretched out on this bare midrib, which it upholsters in silk and stiffens with bits of the leaf woven in, as Mr. Scudder thinks, to keep the denuded midrib from curling. After a little it makes a bundle out of bits of the leaf and fastens this on the midrib next to the uneaten portion; as it eats the leaf it moves this bundle down. This seems to be a method of diverting the attention of any of its foes, which should they start out exploring the midrib and encounter this worthless bundle would straightway turn back in disgust. After the second molt it rests by day on a twig or a leafpetiole. At first the caterpillar is cylindrical in shape though somewhat warty, but as it molts it changes form and becomes most grotesque in appearance.
It is humpy and spiny, and the enlarged second thoracic segment bears two tall branched spines like the pompons of a drum-major. It has several absurd habits; sometimes it rests with its head bent and the pompons touching the leaf and its tail in the air as if it were trying to stand on its head; or it moves fitfully and sometimes trembles and shakes as if it were experiencing a chill. Mr. Scudder says that it leans its head on the leaf or by the side of the stem on which it is resting as if "weary of this world"; and when attacked, swings the head in a "ferocious fashion." The chrysalis is peculiar in shape. The back of the second abdominal segment bears a large excrescence that has been compared to a "Roman nose."
Most of the species are two-brooded in the North, and some of them are three-brooded. The story of a caterpillar of this latest brood is very interesting. It feeds on the tip of the leaf as described, but when about one-third grown it chooses a leaf and eats from the top about a third the way down. It then fastens the petiole of this leaf to the twig so that it will surely stay all winter; then covering the upper surface of the leaf with a film of silk it draws it together lengthwise above itself, making a tube just large enough to hold its precious person; it then lines this tube with silk. This is its winter home, and when done the caterpillar crawls into it head first, the warty last segment of the body fitting nicely the opening and making a living door; and there it renains until the first buds of spring call it out to a vernal breakfast.
In case of the species which are two-brooded the question is, How does this caterpillar know how to make this winter house? It does it while the summer is still warm, sometimes in August when there is no suggestion of cold or winter fasting. Its parents made no such house, and if it inherited the habit it must have been from its grandparents. This is one of the many mysteries of butterfly life which we with our coarse senses are not likely to fathom.