Abstract
Seasonal changes of the population density of spiders were investigated in a paddy field during the period from April to November, 1972. In dikes the density of spiders was only 50 individuals per m2 in April, but increased considerably by September, showing a saw-teeth-like curve with 3 peaks. On the contrary, the density of spiders in paddy fields remained at a very low level during the first two months after transplantation of rice plants. However, spiders began to increase rapidly from July to August, and the resulting high density was maintained until the rice havest. The maintenace of this high density of spiders in paddy fields was closely related to the emigration of spiders from dikes, and to the plentiful availability of their prays. From these results, it was suggested that dikes served as a preserver not only for the spiders but also for their prays and that the abundance of preys was one of the important factors which affect the density of spiders.
