Predaceous heteropterans are among the most abundant species of predators in many agricultural systems. However, we have only a rudimentary understanding of the biology and ecology of these predators in crop ecosystems. The literature is replete with observations of plant-feeding by predaceous species, but the phenomenon has been studied in some detail in only certain groups of the Heteroptera. In general, phytophagy is considered an important factor in allowing predaceous heteropterans to colonize crops before the arrival of prey, and in permitting subsistence during other periods when prey are scarce. However, plant food also may represent an important complement to a carnivorous diet. We summarized a number of laboratory studies in which life-history traits of various predators were measured relative to diets containing prey and plant components. This analysis showed that the benefits of phytophagy are species-specific and are dependent on predator age and the quality of the prey and plant components of the diet. Available information suggests that anthocorids and mirids may be the only predaceous Heteroptera capable of fully substituting phytophagy for carnivory. For example, several Orius spp. can develop and reproduce on plant food alone. Phytophagy alone can support limited development of predaceous species within the Lygaeidae and Pentatomidae. but only subsistence in species within the Nabidae and Reduviidae. Supplemental plant feeding may be essential for development and reproduction of predators feeding on low-quality prey, but may have only minor effects on the life history traits of predators feeding on