In a residential flower garden on Fremontodendron californicum. As I was photoing the wasp I noticed the second insect on its back. The wasp flew to a different location on the same shrub and walked around seemingly unbothered by the bee. After I took several images the wasp flew with the bee still onboard and I lost track of them. I initially presumed that it was a female and a male. It was not until I viewed the images on the computer that I realized it was a wasp and a bee. I think both are females. Any ideas what is going on?