Photo/Illutration The front page of Tsuyoshi Takeuchi's book "Buki wo motanai cho no tatakaikata" (How butterflies fight without weapons) (Provided by Kyoto University Press)

This is the season when fluttering butterflies are a common sight on my way to work. When two butterflies dance around each other in circles, "whirling flight" is the term used by entomologists.

I recently learned that a new, completely unconventional theory about this behavior is now attracting attention.

The proponent is Tsuyoshi Takeuchi, 46, a researcher at Osaka Metropolitan University.

After long pondering why two male butterflies would just keep chasing each other in circles but not attack each other, Takeuchi concluded that the butterfly that happened to be on the scene first couldn't tell the sex of the newcomer, but engaged blindly in a mating ritual anyway.

His theory was published in an international academic journal and won an award from the Japan Ethological Society.

Until then, the accepted theory in the Japanese entomological community was that the aim of the male butterfly that initiated this behavior was to drive the other butterfly, which was essentially intruding, out of his territory.

And the prevalent understanding overseas was that this behavior represented a strategy to wait out the male rival until it became exhausted.

Takeuchi, however, could not quite agree. "Butterflies have no weapons, so how can we be sure they are actually fighting?" he asked himself.

After repeated observations and experiments, he published his theory that male butterflies invariably initiate this mating ritual, irrespective of the sex of the newcomer.

But the international academic community did not immediately accept this new premise. One researcher pointed out, "Butterflies could not possibly be incapable of discerning the sex of other butterflies."

Still, after reading Takeuchi's publication and interviewing him to help me better understand his theory, I found myself being more convinced by his explanation that the butterflies are engaged in a mating ritual rather than a territorial battle.

I do not mean to equate Takeuchi's theory with the Copernican theory or Darwin's theory of evolution, but it is a fact that any groundbreaking discovery tends to be met with stiff resistance.

As a contemporary of Takeuchi, I am excited to imagine the process by which the world will come to accept his theory.

--The Asahi Shimbun, April 19

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Vox Populi, Vox Dei is a popular daily column that takes up a wide range of topics, including culture, arts and social trends and developments. Written by veteran Asahi Shimbun writers, the column provides useful perspectives on and insights into contemporary Japan and its culture.

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