Do bumble bees fly south? Hibernate? Keep themselves warm like honey bees? Why don’t we see them flying around on a warm winter day?
Even though honey bees and bumble bees are closely related (both in the family Apidae) and even though they are both considered social bees, their life cycles are very different.
A mated bumble bee queen overwinters in a small nest in the ground, just big enough for her. The nest is usually 5 to 15 cm below the surface, and the opening is often obscured by mulch or leaf litter. As temperatures get colder, she produces a chemical in her body (glycerol) that keeps her from freezing, and she remains buried all winter.
After she emerges in the spring, the queen searches for a site to use as a nest. Queens can often be seen examining holes in the ground or nests that have been vacated by other animals such as rodents or birds. The queen may go in and out of a potential site many times before moving on or finally making a selection.
Once she has decided on a site, she begins building a nest, laying eggs, and foraging for nectar and pollen. At first, she does all the work by herself, but after the first batch of brood is hatched, the new workers assist in foraging, nest building, and raising their sisters. Eventually, the queen will have produced enough workers that she no longer has to leave the nest, and egg-laying becomes her full-time job.
The size of the bumble bee nest continues to increase all summer and into the fall. But at some point, often late in summer, the queen begins to produce virgin queens and males instead of just workers. These new queens and males will mate with bees from other colonies.
After mating, a new queen will go off and find a place to spend the winter just as her mother did. The rest of the colony including all the workers, the males, and the original queen will perish with the approach of winter. Each of the hibernating queens, by herself, will awake in spring and begin the daunting task of building a brand new colony from scratch.