Spiders are important predators to planthoppers in paddy field. There are many reports on predation function of the predator. But it is still difficult to estimate number of insects predated by natural spider population group owing to their generalist, interference of inter\| and intra\|species, and error of planthopper numbering. However, relative accurate estimation of the insects predated has practical and important meanings for forecasting planthopper occurrence, making control decision, and augmenting...