Elevated CO₂ concentrations can increase plant growth and change plant nutritive value for herbivores. Several reports indicate that leaf-chewing insects consume more foliage of plants grown at elevated CO₂ concentrations than of plants grown at ambient CO₂. Research with additional plant–pest systems is needed to determine if this phenomenon is widespread and if increased insect feeding might affect productivity. Effects of CO₂ enrichment on foliar consumption and population size of Western flower thrips [Frankliniella occidentalis (Pergande)]) were measured on white clover (Trifolium repens L.). White clover infested with thrips was exposed for 24 h/d to ≈396 (ambient) or 745 μLL⁻¹ (elevated) CO₂ for up to 35 d in 10 greenhouse exposure chambers. At elevated CO₂, clover shoot weight and laminae weight were ≈50% greater, and laminar area was ≈20% greater than at ambient CO₂. Thrips population size was not significantly affected by CO₂, but laminar area scarred by thrips feeding was ≈90% greater at elevated than at ambient CO₂. Because of increased growth, however, undamaged leaf area was approximately 15% greater at elevated than at ambient CO₂.