Thanks to John Pontin for pointing out the Rickia infested ant in one of this years Wildlife Photographer of the Year competition. I had the portfolio at home, but hadn't noticed the fungus on the ant. It's a bit hard to tell from the online image, but is really quite clear when it's a bit bigger.
I'm thinking that the ant is probably Myrmica rubra. As far as I know, R. wasmannii has not been recorded on this species before. Perhaps the photographer, András Mészáros, would be able to help establish whether I'm right?
I'm starting to think that R. wasmannii is actually quite common in Europe, but just under-recorded. Has anyone else made Rickia sightings?