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Monarch and Viceroy Butterflies
Nature Bulletin No. 236-A   September 17, 1966
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation

MONARCH AND VICEROY BUTTERFLIES
From midsummer until frost-time, the Monarch is our best known large butterfly. It lazily drifts about and is more often caught by children and amateur naturalists than other butterflies with a zigzag dodging flight. It is apparently free from attacks by birds, presumably because of its bad flavor attributed to the fact that its larvae feed exclusively on milkweeds. Its glowing reddish-brown wings, edges and veined with black, blend with the mellow colors of autumn fields and roadsides .

Unlike other butterflies, no living Monarch in any stage -- egg, larva, pupa or adult -- is ever found in our region in winter. In May, ragged weather-beaten Monarchs begin to appear; now one, then another. Since the previous fall, their frail wings have carried them many hundreds of miles south and back again. This butterfly migrates. It follows the spring back north and lays marvelously sculptured greenish-white eggs on the undersides of tender young milkweed leaves -- acorn-shaped eggs about the size of the period at the end of this sentence. In two or three days these hatch into tiny green caterpillars cross-banded with black and white, with a pair of thread-like "horns" near the end. For about two weeks they feed day and night, shedding their skins as often as they become too tight.

When they are a little over two inches long, they begin to move about restlessly. Each one finally spins a silken attachment to the underside of a milkweed leaf or tree branch or an overhanging rock, grasps it by claspers on its rear end, and hangs head down. In a half day or so it writhes and twitches out of its old skin to leave a pupa -- a smooth emerald-green chrysalis beautifully studded with gold flecks; truly one of nature's brightest jewels, but a helpless thing without mouth, eyes, legs or wings. As the days pass, the chrysalis darkens because the red and black adult is beginning to develop inside. Then the pupal skin splits and, quickly, there is a new Monarch clinging to its old shell, with wings slowly unfurling like sails. For two hours it slowly opens and closes its wings as they dry and spread, Finally it goes fluttering away. That is the miracle of metamorphosis.

Like other butterflies, the adult Monarch uncoils its long tongue and gathers nectar from flowers. However, it seems to have a special preference for the milkweed and plays an important part in their elaborate system of pollination.

The first brood of Monarchs emerges in midsummer and these promptly lay more eggs on milkweeds. Males and females are similar except that the male has a small pouch of scent scales which attract the females. The second brood appears in early autumn but these, instead of laying eggs, congregate into larger and larger flocks until they finally take off for the south to spend the winter. Years ago, one such flock -- a half mile long and a hundred yards wide -- darkened the sky as it passed over one of our western suburbs.

The adult Viceroy Butterfly belongs to an entirely different family of butterflies but resembles the Monarch so closely in color, shape and markings that it serves as a classical example of mimicry in nature. Its larva feed on the leaves of cottonwood and willow trees, and spend the winter, as caterpillars, each rolled up in a leaf. The adult Viceroy is a little smaller than the Monarch, has an extra dark line across the hind wings, and has a single row of white dots in the black wing borders, instead of a double row. It is popularly supposed that its outward similarity to the acrid-tasting Monarch protects it from birds. If so, why is it that the Monarch out numbers the Viceroy a thousand to one in this region.

Maybe, as we humans have discovered, it is foolish to imitate.


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