I live in MD and I have seen these before too though usually not more than one at a time.I don't know what they are but I have heard them called sweat bees but I'm sure that isn't the actual name.

Not a bee at all. But a flower fly, in the Family Syrphidae.

Thank you both for writing.

Jean, you're right, it's a flower fly! thanks. i'm impressed.

i found a webpage that said:
"Although flower flies resemble bees, they can be distinguished by their wings: flower flies (like all flies) have only 2 wings. Bees have 4 wings."

The website also said: "These flies are able to hover in mid-air, much like hummingbirds." That is exactly what my guys do!

and Panzees, you're right too. the webpage said:
"Flower flies are often called "sweat bees" because of their resemblance to bees and because they often land on human skin to gather sweat. Flower flies cannot sting, but there are small black bees in the family Halictidae (also commonly called sweat bees) that also gather sweat, and will occasionally sting humans while they are doing so. Often, an innocent flower fly is blamed for a sting caused by a "true" sweat bee."

the website is about flowerflies in Kentucky, but it's useful even if i live in Maryland.

Thanks again!

Here is a link that might be useful: Flower flies