Bumblebees eat nectar and pollen, both of which are found in flowers. Pollen is eaten mainly by the queen and the grubs as it is full of protein, although the workers eat some too. Nectar is mainly water with different types of sugary substances in it. Honey is just nectar that has less water and so the sugar has become more concentrated.
Pollination happens when a pollen grain from the anthers (male parts) of a flower
is placed on the stigma (female part). The pollen can be carried by wind, an animal, and in some rare cases water to the stigma. Bumblebees are very good at this as :
1. the depend on flowers totally for food (pollen and nectar), so are common visitors.
2. They learn where the nectaries of complicated flowers are, and how to get at the nectar, so visit many species of the same flower. Pollination only happens when a pollen grain lands on the stigma of the same species of flower.
3. They are so hairy, and their hairs are branched, so pollen sticks to them and is easily passes on to the sticky stigma of a flower.
Anything form 3 - 30 bumblebees flying around excitedly outside a nest entrance, and not going into the nest is typical male behaviour of Bombus hypnorum, the tree bumblebee. The males are probably waiting for new queens to emerge so that they can mate with them.