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.

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.