Abstract
The distribution and life cycle of a water scorpion species, Laccotrephes japonensis SCOTT, were studied at 18 stations located at the river margins of the Yamato-gawa Water System in Nara Prefecture. The scorpions were collected only in the middle to lower part of the water system flowing through a rural area. No L. japonensis were found in mountain streams more than 200 m above sea level or in small streams in residential areas. They inhabited only the submerged parts of monocotyledonous hygrophytes (Glyceria sp., Phalaris arundinacea, Paspalum distichum var. indulum, and Isachne globosa) growing at the margins of main channels and in temporal pools formed on vegetated side bars, but were not collected within the stands of reeds, Phragmites japonica or P. communis. The larvae of the 2nd and 3rd instars were found only in June and July within small pools on vegetated side bars. The larvae of the 4th and 5th instars were collected from July to October both at channel margins and within pools on vegetated side bars. Adults were found from April to October both in pools and at channel margins. Neither adults nor larvae were collected from November to March. The significance of such river margin habitats for water insects inhabiting a primarily lentic environment was discussed with a view to the conservation and management of river biota.
