Photo/Illutration An octopus lives amid a rocky area covered by “hoya” sea squirts. (Provided by Yasuaki Kagii)

Journalist Takashi Tachibana (1940-2021), dubbed an “intellectual giant” in Japan, was wont to say that everyone past the age of 20 must “grow” their own brains.

What he meant was that adult men and women should constantly train their brains by providing intellectual stimulation. I am sure many people would agree.

But what would they say if they are told of an animal that eats its own brain once it has reached maturity?

That's the “hoya” (sea squirt), a squishy orange marine creature.

In its larval stage, the hoya is shaped like a tadpole and uses its brain to swim around in search of home. And once it finds its home, it is said to stay put and start feeding on its own brain.

What a strange creature.

I asked Naohiro Hasegawa, a hoya expert and an assistant professor at Hiroshima Shudo University, why it lives like that.

Hasegawa's answer was simple: “The hoya hardly needs a brain because it doesn't move.”

The brain requires all sorts of nutrients to function. But if the animal stays immobile, it doesn't need the brain to think with. And this lifestyle, Hasegawa said, is the hoya's survival strategy.

“It's not that the hoya can't move,” he went on. “I believe the hoya has chosen not to move. And as a researcher, that's what I find so interesting.”

From the standpoint of humans who have “flourished” by developing their brains, the hoya's lifestyle choice constitutes "reverse thinking." And yet, this critter is said to be the closest to humans among all invertebrates.

With my almost-60-year-old banged-up brain, I wondered vaguely, “What, exactly, is a creature?”

At my neighborhood supermarket, I found a big hoya from Hokkaido. I prepared it by myself and ate it with a vinegar dressing.

A haiku poem by Ryuta Iida (1920-2007) goes to the effect, “I chew hoya/ It rains on pastures and fields.”

From the hoya's fine flavor and texture, I could tell it was in season. And I also learned that the word hoya is haiku's "kigo" seasonal term for summer.

—The Asahi Shimbun, July 25

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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.