The queen mates in the Fall, and only the fertilized queens will survive. The fertilized queens will forage and feed to build up winter stores, and then seek out underground shelter to enter diapause (dormancy) for the winter. When Spring arrives with warmer temperatures she awakes and begins building wax cells, in which she lays fertilized eggs, which will become female worker bees.
She forages until she fills a honey pot, which she has built out of wax, for her to feed on until the eggs hatch. She visits up to 6000 flowers just to fill this honey pot provision for herself! The honey pot will give her the energy she needs to keep the eggs warm by vibrating her flight muscles. She must sit on top of the egg cells to keep them warm until they hatch, which will be four days. Could you imagine shaking for four days? She has some serious endurance!
Here is a fantastic photo of a queen warming her eggs with a honey pot on the left. Provided by: http://dkphoto.photoshelter.com.
She places a pollen provision at the bottom of the cells, and lays eggs on top. She will then lay on top of the eggs to keep them warm. The stacked and disordered arrangement of bumble bee cells makes sense if they need to be warmed by body heat; there’s only so much space one bumble bee body can warm. Once the eggs have hatched, and the larva begins to pupate, she begins foraging and feeding them until they are adults and can assume these rolls in her place.
These young females become her working force for the season. Interestingly, these worker bees, unlike honey worker bees, can lay eggs, but the eggs will only ever become males. Only fertilized eggs become females, and the queen is the only one who can lay female destined eggs.
The worker bees form new cells for the queen to lay her eggs. Each cell contains a pollen provision for the developing larva to feed on, and the worker bees will feed nectar to the young through a hole in the top of the cell. It will take between 4-5 weeks for a bumble bee to develop from egg to adult.
More on this super cool species tomorrow!