Bees on comfrey. There are lots of big stands of this robust perennial growing in many places near me – right outside my front door for one! – and the bumblebees absolutely love it. They often chew a hole in the top of the flower to access the nectaries and I do find that these plants don’t have many viable seed. They are collecting pollen too though so there must be some cross-pollination occurring.
Some might argue that it is too thuggish for a border but I happen to love it (even if the postman struggles to get through).
I am letting the comfrey grow up in my new chicken enclosure too as hens seem to enjoy the rather prickly leaves, as well as the nettles: both are really nutritious.
Wayward Bee 
We’ve got comfrey and Borage outside the back gate and it is like a Bee Heathrow! The Comfrey is heat liquid fertiliser and compost accelerator too. ATB, John
Ah yes – I never get any for the compost heap as the ducks eat it all 😄 it is a great plant – such copious and nutritious nectar.
Lose all mine to the ducks too! Had to move it to inside the fenced garden space, ravenous creatures they are!
Haha! yes they love it!