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This Butterfly, among Nature's Dazzling Jewels, Begins Its Life on a Passionflower

Fluttering over a passion-flower vine, the butterfly flashes brilliant orange and black on the downstroke of its three-inch wings, silver-red on the upsweep. A female gulf fritillary, the butterfly lightly brush-es sensitive receptors in her feet across a vine leaf. Moving along the vine, she hovers against the face of other leaves, skimming each with a light touch. Selecting a leaf, she settles upon it. Now motionless, her wings reveal black circles speck-led on the orange, some of them riveted dead center with white dots. When she rises, she leaves behind a tiny yellow egg case affixed firmly to the passion-flower leaf. The female gulf fritillary will live for another week, perhaps two, but during that time she will deposit dozens of eggs on other vine leaves. Gulf fritillaries range throughout southeastern Arizona during warmer months, when the adult butterflies feed on the nectar of zinnias and marigolds. Although not so common in winter, they are sometimes seen feeding on the nectar of such hardy flowers as lantana and rosemary. But the passionflower vine is the only plant on which the gulf fritillary deposits its eggs. Were there no passionflowers, there would be no gulf fritillaries. The butterfly's fastidious selection of food for its growing caterpillar is justified; passionflower leaves are poisonous to many predators, somewhat protecting the gulf fritillary at every stage of its metamorphosis. Although three species of passionflower vines grow wild in southern Arizona, it was not until gardeners began cultivating them that gulf fritillaries became regular urban visitors. Some butterfly and gardening enthusiasts prefer the more showy but short-lived flowers of hybrids; others favor native plants for their smaller, more abundant flowers. The gulf fritillary lays eggs on either. Glisteningly jewellike and bright yellow when first laid, the gulf fritillary egg begins gradually to darken, becoming black just before the caterpillar hatches. The caterpillar's mission is to eat, and the first thing it eats upon emerging is its own egg case. Next it starts on the leaves of the passionflower vine, gorging itself until its skin or exoskeleton nearly bursts. Then the caterpillar molts, shedding its old skin to reveal a shiny new one beneath. Eating and molting, the caterpillar undergoes four molts, always eating the old skin. On its fifth and final molt, the caterpillar becomes a chrysalis. Of the four metamorphic stages, the larval, or caterpillar stage, is the longest. During this period, energy is stored for the last great change, the transformation from fat, spiny, sluglike creature to delicate, ethereal butterfly. This happens during an episode in the butterfly's natural history called the pupa, or chrysalis. To begin, the caterpillar spins a silken pad onto a stem of the passionflower vine. It then attaches its tail to the silken pad, which will become an anchor point for the chrysalis. The caterpillar slowly releases its grip from the stem. Then, securely attached by silken threads, the caterpillar hangs upside down from the stem and sheds its old skin. The new skin underneath becomes the cuticle, or shell, of the chrysalis. Suspended from a tiny twig by a few silky filaments, the chrysalis appears dormant, in contrast to the fat caterpillar daily devouring its own body weight in passionflower vine leaves. But inside, a remarkable transformation is occurring. First, what was a caterpillar becomes a kind of yellowish soup. Then, thanks to certain "organizer" cells that seem to marshal other cells into action, butterfly begin to take shape. Through the tough but translucent cuticle of the chrysalis, the features of the adult gulf fritillary become identifiable: a wing, a vague orange hue, and the checkered spots that give the butterfly its name, fritillus, "dice box" in Latin. Increasingly, the creature inside the chrysalis takes form until one morning, under a warm sun, the outer sheath cracks and a butterfly emerges. When it is fully hatched, the adult butterfly undergoes one more crucial alteration. Its wings, flimsy and weak when it emerges, must become fairly rigid instruments of flight. To do this, the butterfly fills the wing veins with blood and pumps them full of air. A few tentative wingbeats, and the gulf fritillary launches itself. Once aloft it wastes no time finding a mate. With each flap of its wings, tiny scales are released into the air. In males these scales are "love dust," filling the air with pheromones. And the entire cycle starts anew.