Embryonic patterning is insensitive to embryo size. Consequently, despite size variations among individuals in a population, their body parts are proportionate or ‘scaled’. But how is scaling achieved and do similar mechanisms control within-species and between-species scaling? On p. 2741, Jun Ma and colleagues use embryos from Drosophila melanogaster lines selected for large and small egg volumes to investigate the within-species scaling of the Bicoid (Bcd) morphogen gradient. They show that large embryos contain more maternal bcd mRNA than small embryos and, as a result, have higher anterior nuclear Bcd concentrations. This difference in the anterior production rate of Bcd leads to the scaling properties of the Bcd gradient. That is, in broad regions of large and small embryos, similar Bcd concentrations are found at the same relative embryonic positions. Thus, propose the researchers, unlike between-species scaling, which probably involves species-specific differences in Bcd diffusion and/or decay rates, within-species Bcd gradient scaling depends on the scaling of Bcd production rates with embryo volume.