Spiranthes cernua (Nodding ladies'-tresses orchid)

I was out taking photographs of the small patch of Nodding ladies'-tresses orchid in my front yard bog garden, when a pollinator came buzzing by. It was a huge bumble bee. It began at the lower flowers on each stem and worked its way up, visiting each one in succession. I waited about ten minutes, and it came back again, and performed the same behavior -- I guess it didn't get enough the first time...