They are not aggressive at all, only hard to capture in an image because of their constant movement.
All the bees were about the same size; they were worker bees. Then one huge bee came into the bush - I'm pretty sure it was the queen bee.
The queen is larger than all the workers, and she's the only bee in last year's colony to have overwintered underground, surviving to start this year's colony.
These bees do sting, but they are not aggressive, so look for them this spring and keep an eye out for the big queen!