The Environment Ministry said Thursday that a species of small butterfly endemic to southern Japanese islands is feared to have gone extinct as all artificially-bred butterflies and worms of the type have died.

In the butterfly's natural habitats, located in the Ogasawara Islands some 1,000 kilometers south of Tokyo, no individuals from the species have been confirmed since 2018, the ministry said.

Unless the blue butterfly measuring just over 1 centimeter in length is found in the wild, it will be the first butterfly species native to Japan to go extinct.

A butterfly endemic to Japan's Ogasawara Islands (Photo on courtesy of Tokyo Zooloigical Park Society)

The ministry believes that a decline in the butterfly population is at least partially attributable to foreign lizards on the remote islands.

Efforts to preserve the butterfly species, known as Celastrina ogasawaraensis, had been underway since 2005 by Tama Zoological Park in western Tokyo and also at a facility in Shinjuku Gyoen National Garden in the capital since last October.

But all the butterflies and worms raised at these facilities died in July and earlier this month, the ministry said, adding that repeated inbreeding might have led to an accumulation of hazardous genes, ultimately causing death.

The small butterfly is currently categorized as endangered on the Environment Ministry's Red List. The ministry is expected to decide whether the species should now be listed as extinct.

Photo taken from a Kyodo News airplane shows Chichijima, part of the Ogasawara Islands in the Pacific, about 1,000 kilometers south of Tokyo. (Kyodo)

The Ogasawara Islands are known as the Galapagos Islands of Asia due to their unique flora and fauna after eons of separation from any continent.

While the remote islands are growing popular as a tourist spot for beautiful subtropical scenery and whale watching, limited access via a 24-hour ship voyage available only once once per week helps to preserve the wildlife and natural ecosystems.

The volcanic islands, now administered by the Tokyo metropolitan government, belonged to the United States after World War II before being returned to Japan in 1968.