Benefits of trophobiosis betweenPheidole megacephala(F.) andCoccus viridis(Green) were studied in exclusion experiments in coffee. Treatments consisted of trees with ants and no scale natural enemies, no ants and no natural enemies, natural enemies and no ants, and ants and natural enemies. Ant foraging activity and scale populations were monitored weekly. There were no significant differences in green scale populations between ant-infested and ant-free trees when natural enemies were excluded. This demonstrated that scale survival was not due to sanitational benefits from the removal of honeydew by ants. Scale populations on ant-free trees with natural enemies were significantly different from those on ant-infested trees with natural enemies after 119 d. Ants had a positive influence on green scale survival by interfering with or preying on natural enemies. Ant foraging activity, and scale, coccinellid, and parasitoid densities were monitored on ant-infested and ant-free trees in a second experiment using different ant exclusion techniques. The results were a significant positive interaction between ants and scales and a significant negative interaction between ants and coccinellid larvae. There were no significant interactions between ants and adult coccinellids or parasitoids. Green scales declined after 50 d and were not present after 70 d on trees from which ants were excluded, but scales remained on ant-infested trees. This decline followed increases in four species of larval coccinellids. It was concluded that ants were necessary for the survival ofC. viridisin coffee. In the absence of ants, natural enemies, primarily larval coccinellids, eliminatedC. viridisfrom trees.