Although the Hymenoptera represent a remarkably diverse and socioeconomically important group that is of considerable interest in genome biology, they remain understudied in terms of genome size. This study reports new genome size estimates for 89 species of ants, bees and wasps, representing 17 families and four superfamilies. These are used in a test of the hypothesis that genome sizes are constrained by traits associated with parasitism or eusociality. Not all parasitoid wasps exhibit small genomes, though a relationship based on specific types of parasitism may still occur; by contrast, there was no convincing evidence of a constraint relating to eusociality. The data provided here can be used to guide future research aimed at understanding the evolution of large-scale genomic properties in this order.