~200 spp. in our area, ~600 spp. worldwide(1)
mostly holarctic and neotropical (a few spp. in SE Asia); in our area, all but 4 spp. in the US, 91 spp. in Canada(1)
Extremely difficult to ID to species, even under the microscope. They are so morphologically monotonous that breaking them into species groups is only an option for some. Many species can only be IDed by the relative density of punctures on the surface of the bee.
However: "The limiting factor is resolution of the images. If we could clearly see antennal proportions and scutal sculpturing many species identifications would become possible." (Comment by John Ascher).
Male and female