Different species of bumblebee have different ‘tongue’ lengths, which suit them to different shapes or types of flowers. The plants they are attracted to may flower at different times, which means the queens start their nests at different times in the season. This helps to divide up the available food resources so they all get a share. But it does mean that they need a wide range of suitable flowers over a long period to keep a colony going.
Buff-tailed and White-tailed Bumblebees, for example, have relatively short tongues so prefer to forage from short, open, daisy-like flowers such as red clover and comfrey. In contrast, the Garden Bumblebee has a much longer tongue so can visit flowers with petals that form long tubes such as honeysuckle and white deadnettle. However, some of the short-tongued bumblebees 'cheat' and manage to access deeper flowers by biting a hole in the base of the corolla and stealing the nectar!
Newly emerged queens can't dig underground cavities for themselves, so there is stiff competition for nest sites. Queen bumblebees will sometimes even fight each other to the death to secure a good spot. A shortage of rodent burrows in gardens due to cats, foxes and pest control has made the situation worse. It has been estimated that up to 80% of newly-emerged queens die without successfully founding a nest.