The saying “you are what you eat” is particularly true for female honey bees, which grow up to be either small, sterile workers or large, fertile queens depending on their diet. Previously, many researchers thought that something in the food fed to young queens—a secretion called royal jelly—was what made the difference. Now, a new study suggests it’s signaling molecules in the grub of young worker bees that keeps their sexual development in check. That diet, a mixture of pollen and honey called “beebread,” is shot through with a special kind of microRNA (miRNA), noncoding RNA molecules that help regulate gene expression. To find out whether these miRNAs were the culprit, scientists added them to the diet of larvae raised in the lab. These larvae developed more slowly, with smaller bodies and smaller ovaries than larvae fed food without the supplement, the team reports today in PLOS Genetics. The researchers also found that one common, plant-derived miRNA in beebread switches off a gene that helps larvae turn into queens. After being eaten with food, the miRNAs might enter the bee’s gut and spread throughout the rest of the body, where they could help regulate key genes, the scientists say. Although plant miRNAs alone aren’t likely to turn queens into workers, queens-to-be probably don’t want to eat the commoners’ bread.