What should I do about the bumble bees in my back yard?

There seems to be 1 bumble bee hovering right outside my door. I was observing the bee and it would attack every flying insect that came 10 feet near it (butterfly and otherbees) and then return to its spot. I was within 3 feet of it and it would not attack. I'm curious, because i've heard rumours that they can't sting, should I eliminate this bee? Because I feel it is guarding something like a hive and I don't want more of these guys flying all around my backyard.What should I do about the bumble bees in my back yard?
Bumble bees are generally passive. They are good pollinators too. With the decline in honey bees it is probably a good idea to let it be.