Abstract
The population density of L. pseudoannulata in a paddy field was estimated by the following methods: a direct observation, an enclosing method enclosing each rice hill entirely with a net and various marking-and-recapture methods. Among the marking-and-recapture methods, the one proposed by IWAO et al. (1966) seemed to give the most valid estimate for the total number. The sampling efficiencies for the female adults of the direct observation and the enclosing method were 55% and 89% against the best estimate obtained from the IWAO et al.'s method, respectively. These sampling efficiencies seemed to be applicable to the population involved all the stages of L. pseudoannulata. The distribution of individual spiders in the paddy field was random in terms of rice hills. The population density, therefore, can be estimated at a precision of 0.2 (=Sx/x) by sampling 100-150 hills even when the mean density (x) is as low as 0.3 spiders per hill.
