A series of surveys have been carried out on the spider fauna of houses in various districts of Nagasaki Prefecture, and on the role played by various spider species as predators of house-infesting insects. In total, 45 species belonging to 37 genera and 22 families were collected, among which 29 species (24 genera and 13 families) were the weavers, and 16 species (13 genera and 9 families) were the hunters. Oecobius annulipes and Theridion tepidariorum were the most common species encounter in the houses surveys, and their seasonal changes in population density and the indoor distribution were investigated in detail. The behavior of the two common wandering spiders in houses, Heteropoda venatoria and Selenops bursarius, was specially investigated. They were found most abundantly in barns, but were also common in living rooms with straw mat floor (tatami), in corridor, in latriums and in kitchins. A variety of insect species were shown to be killed by the spiders; the preys confirmed in the present survey were the members of the orders Collembola, Blattaria, Orthoptera, Isoptera, Lepidoptera, Hymenoptera, Coleoptera and Diptera. The cockroaches (Blattaria) were found to be caught mainly by the wandering spiders, such as H. venatoria, H. focipata and S. bursarius. Mosquitos and chironomids (Diptera) were captured by the wandering spiders such as S. bursarius, Hasarius adansoni and Plexippus paykulli, and trapped by the viscid lines of weavers. Houseflies (Diptera) were observed to be killed by most of the house spider species, especially by the wandering ones. In an observation on the predation of a wandering spider, S. bursarius, a total of 42 winged ants, 22 chironomids, 6 houseflies and 2 cockroaches were found to be sacrificed while the author had watched it for 4.5 hours every night for 11 consecutive days.