"These curious little cases may be commonly found upon our willows and poplars in the winter time. I have examined hundreds of them and although they are invariably built upon this plan, they vary greatly in the degree of perfection which the architect attained; and this is especially the case where they have been built in confinement. The blade on the tip piece is sometimes gnawed off right down to the rib; at others it is left almost as broad as the tube. Sometimes it is bent over the orifice; at others not. They are also much more irregular and ungainly when made with broad leaves, such as those of the silver poplar, than when made from the more narrow leaves of the willow tree. These autumnal larvae have also another peculiar habit: they exhibit a tendency to build from the time they are hatched and will always eat the leaves from the side, gnawing large holes and cutting along the sides of the midrib. They commence at the tip, and as they work downward toward the base, they collect the débris into a little bunch which they fasten with silk to the midrib. When the hibernaculum is finished the seam is perfectly smooth and the hole inside is lined with silk. The larva, having completed its work, composes itself for the winter with the hind end toward the orifice. Here it remains till the catkins are in bloom the next spring when it retreats from its house and commences feeding. Not the least wonderful part of this phenomenon is that it is only the autumnal brood of larvae that form pitcher-like houses to live in during the inclement season of the year—the summer brood having no occasion to shelter themselves from cold." It is an interesting fact that in most northern regions these winter cases are nearly always made so near the ground that they are protected by snow during most of the winter.
When an insect has such a curious habit as that of making these winter cases it seems comparatively easy to explain it as an acquired instinct brought about through the conditions of life during the long period in which successive generations have been laid. But, as Doctor Riley seems to suggest above, it is much more difficult to explain this sort of phenomenon when it occurs only in one of two or more broods during the season.
The Banded Purple
Basilarchia arthemis
None of our common butterflies shows more striking color markings than the Banded Purple. A broad white stripe runs midway through the wings on both surfaces, the white making a strong contrast to the purplish or brownish black of the rest of the wings. This white band is supplemented by rows of fulvous and of blue dots, especially on both surfaces of the hind wings.
This butterfly is a northern form ranging to a large extent north of the regions occupied by the Viceroy. Its life-history is very similar to that of the latter insect. The caterpillars have the same curious habits and bear a close general resemblance to one another. The Banded Purple butterflies appear in June and lay their eggs in July upon the tips of the leaves of birches, especially the black birch. Almost all of these eggs are laid within two or three feet of the ground. They are of grayish green color. The caterpillars are greenish- or olive-brown.
About a week after the egg is laid it hatches into a small caterpillar that feeds upon the sides of the leaf and rests upon the midrib just as the Viceroy caterpillar does. It continues to feed through July and the early part of August, moulting once or twice before it begins to form the winter case. It usually goes into this during the latter part of August, when it is in the second or third caterpillar stage. From then on it remains quietly in its winter home, being covered by the deep snows during several months, and coming out about the middle of the following May, when the spring warmth starts the buds of its food plant. It then feeds for two or three weeks before it changes to a chrysalis to emerge in June as a butterfly. There seems to be normally but one brood each year although under exceptional conditions some of the eggs laid in July mature into butterflies the same season. But it is probable that these butterflies either do not lay eggs and perish as the cold comes on, or that if they do lay eggs the caterpillars that hatch from them do not get large enough to construct their winter cases. Consequently, it is doubtful if we can consider the insect really two-brooded even in part.
The Red-spotted Purple
Basilarchia astyanax
Were it not for the wonderful iridescence of its wings the Red-spotted Purple would be one of the most plainly marked of the Sovereigns. But the upper surface of both pairs of wings is thickly covered with iridescent scales which give the insect a shimmering beauty that makes it conspicuous among northern butterflies, suggesting something of the marvelous coloring of the large tropical species. The general coloring is a purplish black with rows of white dots along the borders of the wings. The under surface shows much more of the fulvous brown which is so characteristic of the Viceroy, the brownish background being rather thinly overlaid with iridescent scales, but with a large number of spots and stripes, where the fulvous color alone shows.
The favorite food plants of this species belong to the great order Rosaceae which includes the apple, pear, cherry, rose, and many other common trees and shrubs. The egg is laid upon the extreme tip of the leaf, a characteristic habit of all the species of Basilarchia. It obviously must have decided advantages in preserving the eggs from attack by ants, spiders, Ichneumon flies, and other enemies. All of these creatures are constantly patrolling leaf surfaces in search of eggs and minute insects. They are much more likely to find their victims upon the broad general surface than upon the extreme tip of narrowly pointed leaves. The eggs of all these butterflies are small, and pitted much like a tiny little honeycomb with a large number of tiny hairs arising from the surface. These hairs are very similar to the hairs upon the surface of many leaves and they probably assist in leading other insects to overlook the eggs. Yet, notwithstanding these devices for protection, it remains true that a large proportion of the eggs are attacked by tiny parasites and probably many others are eaten by ants and spiders. This very fact emphasizes the necessity of such protective features as the laying of one egg in a place upon the tip of a leaf and the hairy covering on the egg shells.