What is the name of a bee that looks like a bumble bee, but has a fan shaped hind quarter with a round area on

I live in West Virginia, and see this bee with bumble bees on my butterfly bush a lot. I have never seen anything like it.The top half of it looks like a bumble bee, but the bottom is solid black, has a sort of fan shape, with little, round things at the bottom of either side of the Fan . Does anybody know what it is?What is the name of a bee that looks like a bumble bee, but has a fan shaped hind quarter with a round area on
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