延岡市　Nobeoka-City

The firefly is an insect belonging to the Trypoxylus dichotomus (Rhinoceros beetle) family, with 3 pairs of legs and a body divided into 3 parts: the head, chest and abdomen. It is said that at present approximately 3000 types exist all over the world, with 44 of these types having been confirmed in Japan.

During its lifetime, the firefly changes from an egg to larva, then to a chrysalis and finally an adult, the stage that we generally see when we see them. Also, around the world there are many different kinds of fireflies, such as ones that grow as large as 8cm, ones where the light emitted by the male and female differ, and some that do not grow wings, even as they become adults. It is expected that many new types will be discovered in the future. However, on the other hand, due to serious global environmental damage, many types are becoming extinct and measures to protect them in certain areas have become vigorous.

The word 'Hotaru' was first recorded in the Nihon-Shoki (oldest chronicles in Japan) in 720AD and was already known with the kanji「螢」 during the Heian Period (794-1185AD). There are many different explanations about the origin of the word 'Hotaru', but here are two of them.

The first explanation is that the 'ho' is from the word for fire, 'hi', and the 'taru'is from the word that means to hang down 'tare', namely that people thought that the firefly when lit up looked like an insect that had fire hanging down from its body.

The second explanation is that people in the olden days really thought that 'Fireflies are creatures that have fire flowing out from the tips of their tails' and thus called them 'Hitaremushi' (fire-flowing insect), 'Hitare', 'Hotare' and thus the word 'Hotaru' came to be.

Therefore, we do not really know the origin of the name 'Hotaru', but it is something that has provided a mysterious unchanging spectacle for those watching over the years.

There are many different types of fireflies that lead very different lives, such as those that live on land for their whole lives or those that live underwater only during the larva stage. Here I would like to explain the life of the Genji and Heike fireflies, which are also famous all over Japan. These two types are rather unusual, even from a worldwide perspective, since they are fireflies that live underwater for only the larva stage.

Most types of fireflies must feed during their larva stage, but once they become adults they live only on moisture. So let's take a look at what kind of things the larvae feed on. The larvae of the most famous firefly in Japan, the Genji firefly, feed on the snails Semisulcospira libertine that live underwater. The larvae of the Heike firefly, which live in rice paddies, irrigation channels and wetlands, feed on Viviparadae pond snails, Semisulcospira libertine snails and Radix auricularia japonica snails etc. Besides these, the terrestrial Hime (princess) firefly feeds on Allopeas clavulinum snails and Bekkochlamys perfragilis snails etc. and the Oba (old lady) firefly, which lives in the mountains and forests, feeds on small animals. We can say that fireflies choose feed to suit their living environment.

It is well known that there are many different varieties of firefly, from ones that emit a weak continuous light to those emitting strong intermittent flashes. There are also different varieties that have light-emitting larvae, varieties that do not light up when fully mature, and varieties where the colour emitted by the male and female differs. Furthermore, there are some types of firefly, like the Genji firefly, that light up all the way from the egg stage, through the larva, chrysalis and finally the adult stage.

To explain, fireflies have different light-emitting devices and methods of lighting up that they use for different situations, depending on the purpose of the action. For example, it is thought that the reason why eggs, larvae and chrysalises light up is as a warning to predators whereas adult fireflies light up as a signal of their attempts at communication. Fireflies that do not light up are suited to conducting their activities during the day, and so they use smells as signals instead.

Firstly, the parts that emit the light in fireflies include the reflective layer, epithelium, light-emitting cells, the trachea and neurons. A complicated oxidation reaction occurs in these light-emitting cells between a substance called luciferin and an enzyme called luciferase, as well as adenosine triphosphate (which is characteristic to all living creatures, known as ATP), a miniscule amount of magnesium and some oxygen.

Usually, oxidation reactions produce heat but in the case of the fireflies, there is mostly no heat produced, but light instead. The light emitted from the light-emitting cells are reflected by the reflective layer, and highly efficiently emitted to the outside through the transparent epithelium.

This is the sort of mechanism that gives out light from fireflies but this light does not always stay constant; it may get brighter or go out. In other words, the flickering repeats but because this mechanism is exceedingly complicated, the exact details still remain undiscovered.

The activity of the fireflies is most vigorous at three different points during the day: 7:30-9p.m., around midnight and then around 2a.m., so the best time to watch them is probably between 7:30p.m. and 9p.m. As it starts to get dark just after 7p.m. you'll begin to see the odd light here and there, and then you'll start to see light as though they are gathering into a big group. This simultaneous flickering in a group setting is a trait of the Genji firefly. The peak of light activity is around 8:30pm and from the period after 9p.m. if they have found a mate, you can also see fireflies stopping on the grass and entering the mating period. However, since fireflies are sensitive to light and sound, let's watch them quietly!

You can see many fireflies on dark nights when it is lukewarm, with no wind and no moonlight, but on days when the wind is strong or the temperature is low they hide in the trees and bushes and keep still. Also, they do not usually fly around places where there is artificial light, and tend to prefer dark places. On rainy days, there is a sharp decline in numbers.

So for watching fireflies, it is best to choose a day when it fine or cloudy and when the warm winds are not too strong.

You can tell this by looking at what kind of places have large numbers of fireflies flying around. For the terrestrial fireflies, it is necessary to leave them the natural environments of woods, forests and fields etc., but for the aquatic fireflies, they require rivers, paddy fields and irrigation channels etc. So amongst all the different kinds of fireflies, what kind of conditions are required for the rare aquatic Genji firefly?

The first condition is the presence of overgrown trees and grasses on the riverbank and water's edge, where the fireflies can lay their eggs. It is a place where its natural state has been preserved and unchanged since long ago. The second condition is that the water must be of good quality, providing a good nutritional balance and a place where the larvae's feed Semisulcospira libertine can grow. The water must also flow safely all year round, even throughout the winter period. The third condition is the presence of an embankment or sand where the larvae can go underground, once they move onto land. The fourth condition is that the water's edge, where the fireflies flutter around, is a dark place where there is very little artificial light from car headlights or streetlights etc.

Conditions such as these have become requirements for the fireflies to continue their habitation but this is not only limited to the fireflies - surely we can say that it is an essential environment for us as humans as well.

You can search in the library or ask someone who knows a lot about fireflies, but if you have time, please come to Kitagawa! There is a museum/resource library called 'Firefly House' in Kitagawa Machi, and you can learn in great detail about fireflies and the river where they live. There are images and materials on display that can usually not be seen, and within the building, firefly breeding is also taking place. Furthermore, if you speak to the manager, Mr. Jikumaru, I'm sure he will tell you many interesting things about fireflies.