Osmia taurus, an introduced species that's displacing some of our natives. Because of this and other introduced mason bees, most experts seem to be on the fence about recommending Mason Bee Tubes (such as those sold by Knox Cellars Native Pollinators). The idea being such sites would allow the nonnatives to gain access to other locations they haven't reached. At the same time though they provide nesting for natives as well. Unfortunately this is a topic that needs more study. O. taurus is abundant in my area but I still have native species, and presumably 2 other species nesting alongside them.
A major reason to discourage nonnative bees is they sometimes specialize in pollinating noxious weeds. The Giant Resin Bee, Megachile sculpturalis, is an introduced species from Asia. It's basically an overgrown leaf cutter bee that goes right for plant resin instead of cutting leaves. It's also a more suited pollinator of the dreaded Kudzu, Pueraria montana. Kudzu used to rarely produce seeds as very few of our native pollinators were managing to pollinate the flowers, though I'm sure many were able to steal nectar from it.
As things leaf out we'll start to see real leaf cutter bees flying around. These nest in both underground holes and in preexisting tubes. They're set apart from digger and mason bees in that they cut slices out of leaves to make chambers, instead of using mud or simply burying their young. Over the summer I'll also be keeping an eye out for Squash Bees, Sunflower Bees, and Rose Mallow Bees. Also buzzing about now should be Blueberry Bees; all of whom specialize in flower shapes that their common names suggest.