Ecological stoichiometry has spawned renewed interest in the nutritional ecology of terrestrial insects. Classically, research has focused on species’ nitrogen economies and has focused on variation in ‘supply’ (e.g., nutritional differences within and among plant species). However, recent discoveries have made clear that tremendous variation also exists on the ‘demand’ side. Both broad surveys and taxon-specific studies (e.g., ants) have revealed that predatory species are more nitrogen-rich than herbivorous species. Among herbivores, the more derived phylogenetic orders (e.g., the Lepidoptera) contain up to 30% less nitrogen by mass than do ancestral orders (e.g., the Orthoptera). Other recent discoveries have suggested a potentially important (and underappreciated) role for phosphorus in terrestrial plant-herbivore interactions. Among taxa differences in supply of and demand for nutritional resources can influence both the spatial and temporal dynamics of populations. Examples include the volcanic primary successional habitat of Mount St. Helens (Washington, USA) where plant-herbivore stoichiometry influences the spatial spread of recolonizing lupine plants, and, potentially, outbreaking species of herbivorous forest insects such as gypsy moth (/Lymantria dispar/) and hemlock woolly adelgid (/Adelges tsugae/).