Joseph, bumblebees are so cool. I know more about them than the other pollinators, because when I learned about them in ye olde insect systematics course it blew my mind.
The mated queens overwinter alone. These are the big bumblers you see first in spring, and they are hungry after winter and also gathering nectar for a honey pot to sip while they are brooding their eggs. She eats some pollen too, but pollen is the main food of the larvae all season long.
The funniest thing about bumblebees, every generation of workers is bigger than the last. I always thought the different sizes were maybe different species, but not so. Their size depends on the abundance of resources. So as the season progresses, there is more food for all, and later broods of workers are bigger and bigger. Males and female-queens are produced at the end of the season and of course they are biggest in part because of hormonal differences but also they have the most resources. Winter kills all the bees except for the mated queens, which find a place to shelter underground until spring. North facing banks are said to be ideal sites for us, so the queens don't rouse to search for food before the flowers are out.
Also it is really important to have early nectar sources in the area.
Here's a site that talks about the feeding habits of bumblebees:
http://www.bumblebee.org/lifecycle.htm