While doing fall yard cleanup, I saw all kinds of bumblebees (and carpenter bees) and wondered, "What exactly happens to all these guys?"
Here's the short of it:
Bumblebee colonies don't overwinter. So, before winter, the newly mated queen will find a small nest in the ground, just big enough for her. The opening is usually obscured by leaf litter. Here's a crazy thing: as winter gets colder, the queen produces a chemical (glycerol) so she doesn't freeze and can survive the winter and everyone else drops dead. Nuts.
In the spring, the queen emerges, finds a new spot for her underground nest (some species of bumbles will seek out empty bird houses, mailboxes, whatever) and lays her eggs. Her majesty then flies solo to forage for nectar and pollen. After her first brood emerges, the new workers (who are all female) help in the foraging, taking care of the nest and caring for their sisters. At some point, the queen produces enough workers and just stays in the nest, laying eggs full time.
The bumbles keep multiplying and at some point, late in summer, the queen produces virgin queens and males. These new queens and male bees mate with bees from other colonies. Crazy stuff, I know.
After all the summer and fall fun and after mating, a new queen goes off to find a nest of her own, just like her mother did. Then sadly, as before, everyone - including the old queen, workers and males, all drop dead. The cycle begins again in spring. Nature is somethin' else!
Thanks to Honey Bee Suite for the bumble education!