Tatsuno (Japan) (AFP)

As the sun sets over the small mountain town of Tatsuno (central Japan), thousands of fireflies begin to glow in the dark, an early summer spectacle that normally attracts tens of thousands of visitors.

This year however, the dance of insects took place in privacy: because the organizers of the Tatsuno firefly festival preferred to cancel it to limit the risks linked to the coronavirus pandemic.

This natural spectacle lasts only ten days in June, and constitutes the last chapter of the life of fireflies.

"Over a year of life, the fireflies only shine for 10 to 15 of the last days of their existence to leave behind descendants", reminds AFP the mayor of Tatsuno, Yasuo Takei.

"When we see the spectacle of this ephemeral light, we can only be touched and say that we have to fight to the end. There is perhaps a very Japanese aesthetic vision" of beauty, believes he.

- "Courtship ritual" -

"Light corresponds to a courtship display, it is a means of communication between males and females", completes Katsunori Funaki, head of tourism in Tatsuno.

"It is a tool that will allow them for ten days to find a partner and lay eggs for the following year".

When the conditions are right, without rain or wind, up to 30,000 fireflies perform their intoxicating light ball in this locality of the Nagano region crossed by a river.

"The archives show that a very large number of fireflies could be observed along the Tenryu river from the end of the XIXth to the beginning of the XXth century", specifies the mayor.

But these fragile beings had almost disappeared from the region thereafter, as industries such as that of silk had developed upstream of the river, and with them pollution.

After the Second World War, the city made great efforts to restore the environment and protect the fireflies, and has organized this amazing festival for over 70 years.

- A snail to the rescue -

When these tiny creatures are present in numbers, "they offer a spectacular landscape of light, where stars and sparkling fireflies are reflected in the water," marvels Mr. Takei.

The presence of fireflies is usually a sign of pristine nature, but these insects also have special requirements for choosing their environment.

To attract them, the city of Tatsuno notably uses a freshwater snail called "kawanina" in Japanese (Semisulcospira libertina).

Because fireflies spend about nine months developing in water, and their larvae are fond of this snail, explains Mr. Funaki by showing a ditch filled with these gastropods.

The city has created a park where artificial canals channel pure water from the river and waterfalls to provide an oxygen-rich aquatic habitat.

By taking care of the fireflies, we can "hope that we will again be able to enjoy a beautiful dance next year", launches the mayor, and the organizers of the festival hope that the 2021 edition will be able to be held well.

© 2020 AFP