Abstract
In this paper the distiribution of Plebejus argus BUTLER in the Chugoku distirict is discussed. 1. In this distict this butterfly is distributed mainly in the mountainous region (the Chugoku-sanchi) from Kanmuri-yama (West end of the Chugoku-sanchi) to the line that links Chizu-Cho (Tottori Pref.) with Mimasaka-Cho (Okayama Pref.). It has not been found in Hyogo Prefecture. 2. The larva is fed on Cirsium sieboldi MIQ. in this area, but the factors influencing the distribution of this butterfly are not only food plant, but the presence of the moor. 3. The moors are found at fairly low lands in the Chugoku district, but the habitats of this butterfly in this district are conformable to the distribution of the moor with the association of Cirsieto-Molenietum japonicae in the mountainous region. 4. It is estimated that Plebejus argus extended its distribution from Korea Peninsula to the Chugoku district, and also extended to the northern parts of Japan from Amur and Saghalien in glacial age from Ris G1, to Wurm G1.
