Bee on a dahlia

We have a tub in our garden with some very, very yellow dahlias. Especially when the sun shines on them they are really eye-catching.
Also bee-catching. But only when I am not around. I used my 500mm lens to be away far enough, but this shot is the only one I managed. And I waited patiently, took many pictures of butterflies on the adjacent Buddleja. Still, no further bees.