Bombus pensylvanicus, like all Bombus spp., are eusocial.
True sociality, or eusociality, is defined by three features:
1) There is cooperative care of offspring;
2) There is an overlapping of generations in the colony, such that there are several generations of bees in the nest simultaneously
3) That there is a reproductive division of labor, i.e. not every individual reproduces equally in the group
- Bees and Social Insects (see http://www.cyberbee.net/biology/ch2/)
- The Social Lives of Bees - Beespotter (see http://beespotter.mste.illinois.edu/topics/social/)