It is known that fireflies appear in a broad area, where many fireflies flying up in the river to the shore looks like an ocean full of lights. They say that this is the only area in Kyushu that such a number of fireflies appear in the large area, but this was not made naturally; there was a tireless effort of the residents. By the way, if you go further down the Banjou River, you will find Onagara Limestone Cave and a park with the largest water wheel in Japan always full of tourists. You may have noticed by now, but there was the Inazumi Underwater Cave in the Hakusan River area which was introduced as a great spot for viewing fireflies.
Limestone caves will form where lime rocks are present. Hence, both Hakusan and Banjou Rivers are flowing through the lime rock area. These two rivers are located in the north and south of the lime rock mountains that run diagonally in southern Oita. Lime rock produces clear streams with less turbidity.
But that’s not all. While fireflies grow as larvae in the river, they eat black snails. Black snails need limestone to make their shell. So more black snails will inhabit the river around lime rock, and this will be a great condition for fireflies. When you want to raise fireflies, you would put concrete blocks in water to raise black snails, but these rivers provide the environment naturally.
As for the Japanese fireflies, the most famous is the Genji Botaru (Luciola cruciata) which is about 15mm in length, but in Oita Prefecture we have Heike Botaru (Luciola lateralis) and Hime Botaru (Luciola parvula) which are about half the size.