Bumblebee population declines have been linked to a reduction in nutritional resources due to anthropogenic land-use intensification. However, our knowledge of the nutritional requirements of bumblebees remains limited. While initial studies have ascertained the nutritional requirements of bumblebee workers, no data exist for bumblebee queens, who represent the solitary stage of the bumblebee life-cycle, and are central to the persistence of populations. Post-hibernation, queen bumblebees must forage for themselves before founding a colony. During this key stage of the lifecycle queens must consume the correct quantity and quality of nutrients to achieve optimum fitness and subsequently produce a successful colony. Pollen is the primary source of lipid and protein for bumblebees, but its nutritional quality varies significantly across plant species. Here we tested the capability of queens from two abundant, but morphologically and phenologically distinct species of bumblebees - Bombus terrestris, a short-tongued, early-emerging species, and Bombus pascuorum, a long-tongued, late-emerging species - to regulate their protein and lipid intake. Wild-caught queens were restricted to a range of artificial diets that varied in protein:lipid ratios. By measuring the quantities of each macronutrient consumed, we determined the nutritional intake targets of queens of both species using the Geometric Framework Model. We then compared this to the resources available in the wild for these queens, to determine potential mismatches between optimal and available diets. We interpret our results in the broader context of bumblebee declines, and suggest nutritional interventions that could enhance queen fitness in the modern landscape.