In the roses yesterday at the BBG, the bumble bees were busy. Buzzy, too. Bumble bees, being natives, are better adapted for some tightly bundled flowers because they will "buzz" or vibrate the petals to get into them. These roses are pretty loose, but I could still feel the buzz through the stem. You can open up these images for bigger viewing. Note the pollen packed on the rear legs. The one above is browner, the one below is more orange. The color depends on the pollen they are collecting. The pollen attaches to the bees' hairs, which are statically charged, and the bees rake it off, moistening it with some nectar, and then packing around the convex hollows on the rear legs.
These are obviously bombus, but I don't know the species.