After the eggs hatch (a couple of days after they have been laid) the developing larvae feed upon the pollen provisions and go through various growth stages before spinning cocoons around themselves and pupating. After two weeks in their cocoons they will emerge as fully grown adult bees. The first few broods are alway female 'worker' bees. They are usually much smaller than the queen and will take on the roles of nurse maids, cleaners, guards and foragers.
From this time onwards the queen bumblebee is unlikely to leave the nest.
Knock-on effect for bees
For more information about bumblebees please have a look at the following sites...