Mimic wasp bee

I had a feast of new bugs today - from a leafhopper in a black DJ that actually came out of hiding for a photo to a semaphore fly with beautiful orange compound eyes and white wing tips. 

But this little mimic wasp bee (fairly certain that's what it is), I reckon, is the one I'm least likely to see again (probably tomorrow now!)  Its larvae are internal parasites of bumblebees.