Rummaging on a Purple Flower

I don't what kind of bee this is but they get along with humans just fine.  We have this perennial out back that smells like a weed.  Grows like a weed and pretty much looks like a weed other than the flowers.  It attracts butterflies and these bees every year but mainly this variety of bees.  You never see them with pollen on their legs like you do honey bees.  Between this plant and a Lythrum that is close by I would venture a guess of 35 or more bees.  They stay at the plants and if you reach in to do any trimming it doesn't bother them.