Bumble bees generally visit flowers exhibiting the bee pollination syndrome. They will also tend to visit the same patches of flowers every day, as long as they continue to find nectar and pollen. Pollen is removed from flowers deliberately or incidentally by bumble bees. Incidental removal occurs when bumble bees come in contact with the anthers of a flower while collecting nectar. The bumble bee’s body hairs receive a dusting of pollen from the anthers, which is then groomed into the corbicula (“pollen basket”), as you can see here. These thistles were a big hit with the bumble bees in my yard for as long as they lasted. Many a great photo op was had in that short period of time. This was taken in my back yard in Rockaway, NJ USA with my Nikon D3100 and the85mm macro lens.