Butterfly native to far-flung isles thought to have finally died out

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With no sightings in two years, the rare Ogasawara blue butterfly, named after its island chain natural habitat far south of Tokyo and designated a national natural treasure, is considered extinct, the Environment Ministry announced Aug. 27.

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All Ogasawara blue butterflies bred outside the islands were thought to have died out in August or before due to a decline in reproduction ability caused by inbreeding.

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Specimens measured about 10 millimeters in length and used to thrive in the Ogasawara island chain about 1,000 kilometers south of Tokyo.

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Experts cited the presence of predators such as lizards and non-native species for the decline.

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Before June 2018, a number of butterflies were spotted, but only in Hahajima island, and not since then.

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The Tama Zoological Park in Tokyo’s Hino embarked on a breeding program in 2005 in hopes of securing continuation of the species.

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Since fiscal 2019, the Shinjuku Gyoen National Garden in the capital’s Shinjuku Ward also began to breed them after receiving specimens from the zoo park.

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From this spring, however, the ratio of fertilized eggs decreased dramatically and no more larva emerged. All the butterflies were dead by Aug. 25.

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According to the Environment Ministry’s red list on endangered species, the Ogasawara blue butterfly was categorized as “Critically Endangered,” meaning it is highly likely to go extinct in the wild in the near future.

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If there are no new sightings by the time the next red list announcement is scheduled, probably in or after fiscal 2024, the species will likely be listed officially as the first extinct butterfly indigenous to Japan.

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