You can view here, clearly shows how they inserted their proboscis through the receptacle of the flower.
Bumblebee, considered as the most stinging bees because of their large size. If you hear the word bees, the first thing that comes into your mind in connection with honey and stinging pain but it is useful to humans because of their honey supply.
Being called as an insect pollinator, they are adopted to the flower of their choice. from the 2nd and 4th photos, you can see the bumblebees tuber-like mouth part(tongue or proboscis) to suck up the nectar of their chosen flowers. The nectar is converted within the bee into honey, pollen is mixed with honey or nectar to make bee bread as food of young bees.