Organism grow and reproduce best under a specific set of biotic and abiotic conditions, yet a quick look outside reveals a world that is astoundingly variable. Organisms face massive biotic and abiotic variability and only rarely experience their optimal conditions. How all this variability influences population and community ecology is poorly understood. In this talk, I explore how plant trait diversity affects the performance and population dynamics of insect herbivores. First, I use a meta-analysis to show that variance in plant nutrient levels reduces insect herbivore performance, suggesting that plant diversity suppresses insects, while monocultures benefit insects. Second, I use a natural plant-herbivore system to show that average plant quality can be less important than variance in plant quality for insect population dynamics. Finally, I present preliminary results from a new experimental approach to studying the consequences of trait variability along specific trait axes.