Earth Journal

Vol. 8, No. 27
July 6-12, 2000
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In Season, Life Cycle: Tiger Swallowtail
By Gary Pendleton

Cats are said to live nine lives. Butterflies have two, living as two distinctly different creatures and occupying completely different ecological niches.

The life cycle of butterflies is complex and beautiful with a hint of the mysterious. It involves at least two species of plants and four life stages: egg, larvae and pupae, culminating in a profound metamorphosis to adult butterfly.

Butterflies belong to a highly evolved group of insects called Lepidoptera. Pictured here are the four stages of the Tiger Swallowtail. This black-and-yellow species is a beautiful and common resident of the eastern United States.

Butterfly eggs come in a variety of jewel-like forms. This life cycle begins when the Tiger Swallowtail lays a pearl-like egg on the leaf of a tulip poplar tree. Butterflies are particular about where they lay their eggs. Tulip poplar is the “host plant” for the Tiger Swallowtail caterpillar, which emerges from the egg to eat this food alone.

The caterpillar has a large spot that resembles an eye. The purpose of the eye spot could be to make birds and other small predators think they are dealing with a more formidable prey. The caterpillar is a voracious eater and it grows rapidly, periodically shedding its skin, like a cicada, leaving a chitinous husk behind. The growth stages between sheddings are called “instars.” The transition from larvae to pupae takes place when the last instar sheds its skin and chrysalis emerges.

Before pupating, the caterpillar will have attached itself to a leaf or twig. It is during this sedate third stage that a remarkable transformation happens. In essence, the caterpillar dissolves into a soupy homogeneous substance inside the chrysalis that resolves into the adult butterfly.

When the time comes, the chrysalis splits open and the adult emerges with wings soft and folded. Fluid is pumped through the wing veins, which reach full size and stiffen in a moment’s time. The adult exploits a separate ecological niche from the caterpillar, feeding on the nectar of Joe Pye weed as well as common garden flowers.

It is fun and educational to responsibly raise butterflies in captivity. To learn more read Robert Michael Pyle’s informative and well-written Handbook for Butterfly Watchers, which was a source for this story.

Copyright 2000
Bay Weekly