In recent years, in Japan fireflies (Luciola) have attracted attention as a barometer of water side environments and numerous activities have been undertaken to protect them. However, in many cases the protection of fireflies has met with failure and it remains difficult for fireflies to generate spontaneously. There are many conditions required for fireflies to live and it is very hard to express such conditions in figures. Therefore it is difficult to estimate their living conditions by numerical analysis.
In the first part of this research, the present state of generation and living of the fireflies known as genjibotaru in the Kanto district are investigated. Next, the authors divide the living conditions into three items: flow condition, water quality condition and environment condition. For the numerical analysis for each item, quantification are applied. As a result, the effective living conditions for genjibotaru are established. The results will be great interest to people concerned with the protection of the river environment.