Soil composition affects insects feeding on plants. Here we examine soil iron availability in relation to flight of a butterfly, Melitaea cinxia, which contains polymorphisms in a HIF pathway gene that regulates oxygen delivery to tissues. Iron is a co-factor of the HIF pathway enzyme (PHD) regulated by succinate. We found a strong effect of iron availability on adult flight performance. These results show a novel way that environmental heterogeneity affects life history traits.