Butterflies Worth Knowing

by Clarence Moores Weed

See [page 67]

When full grown the caterpillars find such shelter as they may and each spins a bit of silken web and a silken loop which hold it while it changes to the chrysalis. This chrysalis is very likely to take on the colors of the immediate surroundings and thus be rather difficult to see. If the egg was laid by one of the spring or early summer butterflies, the chrysalis will soon change to a butterfly which will appear toward midsummer and which may lay eggs for another brood of caterpillars. These caterpillars mature to chrysalids the same season and some of them are believed to change into butterflies in autumn, these butterflies hibernating through the winter; while others are believed to remain unchanged through the winter and disclose the butterfly the following spring. This is an exceptional condition for the Swallowtails and it is worth while to make careful observations along its northern limits to learn more definitely the facts as to the winter condition.

The Green-clouded Swallowtail
Papilio troilus

This beautiful butterfly is essentially a southern species and is found over a wide range of territory from the Mississippi River to the Atlantic Ocean. It occurs as far north as New Hampshire and Vermont and has even been reported from Alberta, Canada. It is easily recognized by the blue-green clouding of the upper surface of the wings, the general color being velvety black with distinctive rows of yellow spots along the margins of the front wing. These spots are present also on the hind wing where they are almost changed to blue because overlaid with a general cloudiness of this color. On the under surface of the hind wings there are two rows of orange-brown spots, the inner row being nearly crescent-shaped and the outer row oblong. In the living insect the tail projections on the hind wings are usually twisted into a vertical plane at right angles to the plane of the wings.

The caterpillars of this species feed upon the leaves of sassafras and spice bush. The distribution of the butterfly appears to be closely related to the distribution of these plants.

As is the case with so many of our Swallowtail butterflies, the Green-clouded Swallowtail passes through the winter in the chrysalis stage. Late in spring the butterflies emerge and soon afterward lay their eggs singly upon the leaves of sassafras or spice bush. The eggs soon hatch into lead-colored caterpillars, largely covered with spiny warts. Each caterpillar cleverly makes a protecting nest by eating out a narrow strip in the leaf which frees a flap along the margin that is turned back upon the leaf, making a case in which the larva lives. It spins a silken carpet on one side of the case and rests upon this carpet when at home. During its feeding periods it goes outside and eats the tissues of the other parts of the same leaf. It continues to occupy this first nest for a week or more by which time the rest of the leaf is likely to be pretty well consumed.

Having passed the first moult and thus become larger and having practically eaten itself out of its first house and home the caterpillar now crawls to a larger leaf where it proceeds to make a more enduring structure. In this case it does not need to bite a channel along one side of the midrib as it did before, but instead it begins to spin silken threads transversely across the upper surface in such a way as to fold over the border of the leaf and make a tubular chamber in which it has plenty of room to move about. It uses this as its home for some time thereafter, wandering out at evening to feed upon neighboring leaves as its hunger necessitates. In this way it continues to feed and grow for a week or two. Then it finds it necessary to construct still another home, which it does by bringing together the opposite sides of a leaf, taking care to have a door-like opening at the base of the blade next the leaf stalk. This third home serves it to the end of its larval existence. It goes in and out as necessary, remaining concealed when it casts its skin and until the body tissues harden afterward. Apparently it devours the cast skin and thrusts the hard covering of the head out of the nest. Consequently these little homes are clean and sanitary and serve admirably their protecting purpose.

The full-grown caterpillars have the curious appearance of those of the other Swallowtails. The third ring behind the head is greatly swollen, making, with the rings directly in front of it, a characteristic picture suggesting a grotesque face with large eye-like spots at the top. The general color is green, darker above than below, and there are six rows of blue dots along the body. (See plate, [page 80].)

When ready to change to the chrysalis, the caterpillars desert their leafy homes and on a twig or board or stone each spins a bit of silken webbing and a silken loop. They now change to chrysalids which are likely to resemble the color of the background and which are somewhat smoother than many of the Swallowtail chrysalids. About two weeks later the butterflies emerge.