Understanding why: efficiency, robustness, and division of labor in bumble bees

Social insects show an enormous diversity in their social behaviors, for example in the strategies used to divide labor or forage collectively. To understand why these different strategies evolved, we have to understand their benefits under different ecological and social conditions. Hölldobler's & Wilson's work has initiated the quantitative study of worker polymorphism and division of labor in ants; worker body size polymorphism in bumble bees is far less well understood. Here I show that in addition to division of labor, individual lifespan and colony-level robustness may be crucial traits affected by worker size polymorphism.