Tsushima Island in Nagasaki Prefecture is located approximately halfway between Kyushu and the Korean Peninsula. On a clear day, you can see South Korea from the north shore. This unique location is why the island played a crucial role in the formation of the regional ecosystem, serving as a land bridge for various animal and plant species to migrate from mainland Asia to Japan. To this day, it is home to many plants and animals that can be found nowhere else in the country.
The richness of the island's biodiversity is evident even among small insects. Pithecops fulgens , also known as Tsushima Uraboshi Shijimi , or the Tsushima Blue Quaker, is one of the rarest butterflies in Japan. But the population has plummeted in recent decades, with some estimates suggesting only a small number remain in the wild. Ten years ago, scientists took live specimens of the Tsushima Blue Quaker to Tokyo, over 1,000 kilometers away, as part of a conservation effort.
The Tsushima Blue Quaker
The Tsushima Blue Quaker is tiny, with a wingspan of only about two centimeters. The "uraboshi" in its Japanese name means "back star" and refers to the black spots on the underside of its hind wings that appear when its wings are closed. Tsushima is its only known home in Japan; the closest populations live in parts of Taiwan and Fujian Province of southern China. It has not even been found in neighboring South Korea. The presence of such an isolated species is unusual, even on a land bridge like Tsushima. Scientists are unsure how the butterfly ended up on the island.
According to local butterfly enthusiasts, the Tsushima Blue Quaker was once common throughout the north of the island. But the population has been rapidly declining since the 2000s, with a 2013 survey by the Japan Butterfly Conservation Society only able to confirm one area in which it still lived.
"It would almost certainly have gone extinct if we did nothing," said Yago Masaya, a lecturer at the University of Tokyo who took part in the study.
Yago says the biggest reason for the disappearance of the butterflies is the approximately 40,000 deer that live on the island. Yago says their eating habits pose a destructive threat to butterfly habitats.
"The deer eat up all the plants until the area is barren," Yago says. "The vegetation on the forest floor doesn't recover. This means the grasses that the larvae eat and the flowers from which adult butterflies take nectar are gone."
Yago realized time was running out for the beloved butterfly. Drastic action was needed. He decided to undertake an "ex-situ conservation" operation and temporarily moved some butterflies from Tsushima so they could breed.
1,000 km from home
The Adachi Park of Living Things in Tokyo is home to a greenhouse where specialists raise 8,000 butterflies from 50 species. In 2013, a team from Tsushima brought the latest addition to the site: the Tsushima Blue Quaker.
Mizuochi Nagisa had just started a job at the park. She had studied entomology at university and was a member of a student insect club that bred different species and studied their ecology. Because of this experience, she was immediately tasked with leading the Tsushima Blue Quaker breeding program.
Being entrusted with the future of a butterfly species is a huge responsibility for a new graduate. But Mizuochi says since she was unfamiliar with the Tsushima Blue Quaker, she did not initially grasp the gravity of her mission.
"At first, I didn't know anything about the Tsushima Blue Quaker," she said. "Then after my second and third years of breeding, I finally started to understand the pressure. If I failed, these butterflies might go extinct."
Mizuochi faced many challenges in her efforts to breed the butterflies. The biggest was getting them to mate. For this purpose, breeders typically use two methods. One is called "hand pairing," which requires a breeder to hold a male and female in their hands. The other involves the use of a cylindrical breeding net in which the butterflies are kept until they mate. But Tsushima Blue Quakers turned out to be too small for the first method; the second was also unsuccessful.
She gradually realized the butterflies needed space. The male wanted its own territory in which it could fly. Mizuochi observed that when another male entered this area, the butterfly would chase it out. But when a female entered, it would approach and fly around it. This is called "hovering" and is something male butterflies do when they are trying to mate.
Mizuochi and her team created a process in which they first released the male butterflies into the greenhouse, allowing them to establish their territories. After some time had passed, they brought around females perched on branches. At first, they were only able to mate one or two pairs a day. But Mizuochi learned how to identify which butterflies were ready for mating and was eventually able to increase the number to about five pairs.
Another challenge they faced was the "overwintering" of larvae. After hatching, the butterflies turn into larvae for the winter, but many of Mizuochi's specimens died. In the second year of breeding, only about ten percent of the larvae survived. This rate would not be enough to ensure the survival of the species. Mizuochi and her team experimented with the habitat. They used different types of soil and dry leaves and switched from an unglazed to a plastic flower pot. Eventually, they found the ideal level of humidity that allowed the larvae to make it through the winter months.
This year, the wintering success rate is close to 90 percent and about 260 adult Tsushima Blue Quakers have emerged.
"Overwintering was difficult but I gathered the data to see what conditions worked best," said Mizuochi. "Larvae die if they are too wet or too dry. Most of them died in the first days so I had to do everything I could to save as many as possible."
After ten years of trial and error, Mizuochi has honed her breeding techniques to a precise science.
Homecoming
As the breeding program got underway in Tokyo, people in Tsushima made preparations to welcome the butterflies home. The Natural Symbiosis Division of the Tsushima City government set up fenced-in habitats to keep deer out. They planted grass for the larvae and flowers for the adults.
Shingu Shusaku, the assistant manager of the division, patrols the areas to check for broken fences and changes to the environment.
"If we don't find a broken fence, deer will come in and eat all the plants," Shingu says. "That will make it difficult for the plants to recover so we have to repair them as soon as possible."
Tsushima Blue Quakers in various stages of development are taken to the conservation areas. Larvae, pupae, and adults are all released into the wild.
But the future of the butterflies is still not secured. Changes in the environment mean the number of Tsushima Blue Quakers fluctuates rapidly. Thousands of larvae, pupae, and adults have been returned to Tsushima, but the population is still not as large as the conservationists had hoped.
"It's difficult to maintain a good environment," Shingu said. "Also, the butterflies move unexpectedly. We thought they would stay in the vicinity of where we released them but that hasn't been the case."
But there are signs of hope. In one conservation area, a rare plant found only in Tsushima, Astilbe tsushimensis, began to grow shortly after the deer fence was built. Since it had not been planted by humans, scientists believe it sprouted from roots that had been underground for years. The flowers of this plant are an important food source for adult Tsushima Blue Quakers.
"If we can increase these areas and create a habitat network, I think Tsushima Blue Quakers will be able to breed stably," said Shingu. "It is very difficult to recreate an environment that was once lost. It's not just a matter of simply having plants that feed the butterflies."
Sustainable conservation
Scientists in Tokyo and Tsushima have been working to save the Tsushima Blue Quaker for a decade. But Yago, the conservationist from the University of Tokyo, believes there are limits to what they can do. He says the local community will have to soon take over these efforts, and that tying them into programs that benefit the island economically could ensure their success.
"The purpose of conservation is not just to protect butterflies," says Yago. "Protecting butterflies protects the environment, and if local people feel the benefits of biodiversity from an economic perspective, it will trigger an interest in conservation."
He believes shiitake mushrooms are one such way to link the local economy with butterfly conservation efforts. The mushrooms are a Tsushima specialty and grown by planting spores in logs. This method yields shiitake that are thicker and chewier than those cultivated on fungal beds.
Yards where the logs are planted, or "Hodaba," are typically located in valleys in order to maintain adequate humidity. Many are fenced in to prevent deer and wild boar from entering, which makes them ideal places to release butterflies.
Yago is trying to develop a program that offers shiitake farmers incentives to turn their Hodaba into butterfly protection areas. He got the idea from a partnership between local rice farmers and MIT, a non-profit that preserves the habitat of the Tsushima wildcat. In this program, the farmers implement conservation measures on their paddies and the non-profit certifies their rice as "Wildcat rice."
This May, Yago visited a shiitake farm near a butterfly conservation area with MIT representative Yoshino Hajime. He wanted to tell the farmer about his efforts and gauge his interest in participating.
Kasugame Takayoshi's Hodaba is an ideal candidate for the project. It is large and has vegetation on the ground. But he is uncertain about the future of shiitake farming. The price of log-grown shiitake mushrooms has barely grown over the past decade, while production costs are steadily increasing due to factors such as rising raw material prices. Furthermore, the method is hard work compared to fungal bed cultivation. Kasugame has to cut down the wood, plant the fungi, and line up the logs. It is a physically intensive process that is difficult for farmers to continue as they get older.
"In the past, more than 200 households in this village grew shiitake mushrooms," Kasugame says. "Now, there are only four farms. The hoda trees, which are essential for production, are becoming scarce because the deer eat the seedlings. I can't say I want young people to take over the job."
Yago says this underscores the importance of combining conservation with local business.
"We need the conservation of butterflies to add value to shiitake mushrooms and make them profitable again," he said. "Otherwise, we won't be able to conserve the butterfly."
The future of the Tsushima Blue Quaker
In the ten years since the project at the Adachi Park of Living Things started, other ex-situ conservation efforts have begun at sites in Osaka and Nagasaki. But scientists say this can only be a temporary measure and that the future of Tsushima Blue Quaker conservation in Japan must be based in the forests of Tsushima.
Butterflies are environmental indicators and their presence is often a sign that an area is healthy. In that regard, the plight of butterflies in Japan is a worrying one, as the Tsushima Blue Quaker is not the only species that faces uncertainty. Celastrina ogasawaraensis, or the Ogasawara Blue, which can only be found on the Ogasawara Islands, has not been seen in the field since 2018 and specimens for an ex-situ, breeding program died in 2020. Melitaea scotosia was once common across Honshu, but can now only be found in a small conservation area in Hiroshima Prefecture.
The disappearance of a single species of butterfly can sound the alert for an entire ecosystem. Efforts like those to conserve the Tsushima Blue Quaker are a start, but scientists agree: they must be replaced by more sustainable methods that look for answers beyond the next ten years.
