Pollinator Survey at Taylor Offset. This is very strange and confusing. As far as I can see, there are three bees in the first two photos. A large bee underneeth and two small ones on top. In the third photo (very bad quality because the flash did not fire) there are only the large bee and one small bee remaining. I hope someone can explain this.
It appears to be two male Lasioglossum attempting to mate with a female. The posterior male in the first image is in the typical mating (or premating) position. I can't say to which subgenus they belong. The size difference between the sexes is reasonably common except in species with territorial males, which are very rare in Halictidae.