Social factors influencing the trade-off between egg size and number have been almost entirely neglected in studies of social insects. We examined egg size and number in an Australian allodapine bee where nutritional resource availability and social competition during egg laying vary over colony development. We hypothesised that during August queens should lay many eggs to provide work incentives for subordinates, but because resources are strongly limited these eggs will be small. In spring, resources are less limited but some subordinates also lay eggs, resulting in competition between offspring for communally provided food. Here, we hypothesised that females should attempt to direct resources preferentially to their own offspring by laying large eggs. We analysed egg numbers and weights as functions of colony size. We found that a trade-off existed in August nests but that egg size increased with egg number in October. In November, when larval eclosion was commencing, colonies with larvae had smaller mean egg weights than those with only eggs, suggesting that resources are directed away from oviposition towards larval provisioning. Our analyses suggest that egg size is a function of egg number, rather than colony size per se.