Initially I watched from a distance to assess the situation. All seemed placid, with single bees leaving and returning and no interest shown in me. Shot some rubbishy snaps in case I couldn't get better. Then very slowly over 70 minutes moved slowly closer, getting ever better pics, while watching very closely for any signs of inquisitiveness or aggitation, at which point I would have backed off and called it a day. In the end I got as close as I dared and never had a single bee investigate me.
I would caution against ever approaching a swarm. I was lucky (and probably foolhardy) on this occasion and got some great shots, but I would always take extreme caution in this situation as next time the bees might be in a very different mood!!!
...behind the lens!