Bumbles...

I found these two bumblebees mating on knapweed and in a bit of sunshine. At first I thought they weren't mating as the small one is a male red tailed-bumblebee and the large one is a queen buff tailed bumblebee I think - but it's definitely not a queen red-tailed bumblebee. The queen was also feeding all the time I watched - and so moving around.
I then looked up bumblebees and if they mate other species of bumblebee & found that they generally don't do this. If they do, the resulting offspring are usually infertile...

Was the male red-tailed bee just hitching a ride? Trying to mate or actually mating?

No idea! :)