European bee-eaters Merops apiaster forage almost exclusively on airborne insects caught on the wing. The availability of this food might be temporally limited due to adverse weather conditions, especially at climatically sub-optimal breeding sites. We determined seasonal variation in the diet composition in adult and nestling bee-eaters at the species' northernmost breeding colonies by analysing food remains from pellets and by direct observation. Adult bee-eaters preyed on a wide range of insect species with more than 97% belonging to the taxonomic orders Hymenoptera, Odonata and Coleoptera. We observed consistent seasonal changes in adult diet composition from the pre-incubation to the late chick rearing period. The dry mass proportion of dragonflies decreased remarkably in the adult diet as chick rearing started, whereas the consumption of small Hymenopterans increased by the end of the chick provisioning period. Additionally, we found differences in the diet composition of adults and nestlings. The higher amount of bumblebees and dragonflies in the nestling diet was temporally associated with a decrease of these components in the adult diet, indicating that breeding birds preferentially feed larger prey items to their offspring than those that they consume themselves.