We conducted a field study in September 2007 and 2008 to analyze the foraging activity, natural diets, and predatory efficacy of Tetragnatha javana (Thorell 1890) (Araneae: Tetragnathidae) and Neoscona theis (Walckenaer 1842) (Araneae: Araneidae) on selected prey. The relationship between body measurements (carapace width, leg length, total body length, and body weight) and web dimensions (capture area, capture thread length, number of radii, number of spirals, and mesh height) of both species was also investigated. Most of the observed T. javana constructed their webs between two adjacent rice plants, while N. theis placed theirs at the top of rice plants. Both species required approximately an hour to complete a web, which differed significantly from each other in height, diameter, and capture area. Both species constructed only a single web per day. Web building activity of both species was intense from 17:00 to 18:00, while prey-handling activity was high from 19:00 to 20:00. In both species, peaks of feeding were recorded just after the peaks of prey handling (21:00). The main prey orders caught in the webs of both species were Lepidoptera, Diptera, Homoptera, Coleoptera, Hymenoptera, and Orthoptera. The time required to reach and capture lepidopteran (adults of stem borer and leaf folder) and homopteran prey was similar for both species. However, the time required to reach and capture orthopteran (grasshopper nymphs) prey was significantly longer for T. javana than for N. theis. Capture area increased with carapace width, and capture thread length increased with carapace width and body weight, while leg length and body length did not relate to either of these web variables. The number of radii, number of spirals, and mesh height did not correlate with any of the body size measurements. We concluded that both species can be used effectively to reduce insect pests of rice fields.