The microbial gut communities of social bees are dominated by five bacterial groups. Bees feed on pollen, which contains diverse polysaccharides. Moran and colleagues analysed the genomes of bacterial isolates from honey bees and bumble bees and used transcriptomic and metabolomic experiments to investigate the ability of individual members of the gut microbiota to digest polysaccharides. They identified Bifidobacterium and Gilliamella as the main degraders of hemicellulose and pectin, whereas other gut bacterial species cannot degrade polysaccharides. Moreover, the ability to digest pollen varied between different bacterial strains as well as within and between host bee species. Thus, strain composition within hosts may determine their metabolic capabilities. The authors suggest that core bacteria of the bee microbiota occupy distinct metabolic niches to promote efficient substrate metabolism and their co-existence.