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Biotope in the rain

A few years ago, I took some twigs from the Japanese pepper tree in my garden and put them in a vase. There were eggs and larvae of swallowtail butterfly ('Ageha chou' in Japanese) on them, so I kept them, replacing the twigs as needed, and let them loose once they reached the adult stage. Since then, I think I've grown more than a hundred butteflies in my house.

For Ageha chou eggs that were laid in April through mid-September, it takes one-and-a-half to two months to complete metamorphosis. Caterpillars shed their skin four times on the twigs where the food is, but they usually leave the twigs just before they become pupas, so I move them from the vase to a cardboard box. Many of them that are green on the Japanese pepper twigs become gray once they are put in the cardboard box, demonstrating their mimicry. The pupa stage lasts ten days to two weeks.

In natural environment, Ageha chou caterpillars have many predators and only a few of them grow to become adult butterflies. If, however, all the eggs in my garden survived and grew up as caterpillars, Japanese pepper trees they feed on would lose all their leaves and the caterpillars would die too. Such is the balance kept by law of nature.

Although it is a rare occasion for butterflies to become fossils, they exist to teach us about the distant past. According to the latest theory, butteflies appeared in the Mesozoic Era when dinosaurs were alive, 200- 300 million years after the first insects evolved.

Ageha in my garden lay eggs on Japanese pepper tress and Yuzu trees, and catapillars that are born from those eggs only eat leaves of the mandarin orange family. In the course of 200 million years, butteflies diversified and evolved into various species that only eat leaves of certain plants. It is believed that this is the result of competitive evolution between the plants and the butteflies. Trees of the mandarin orange family evolved to produce specific poisons to defend themselves from insects that feed on them, and ancestors of Ageha butteflies evolved to be resistant to these specific poisons. As this competitive race of evolution progressed, many of the other species stopped feeding on mandarin orange, making it advantegeous for Ageha to specialize on this specific plant.