Bee swarm

Holding on to the pear tree we have possibly thousands of bees all clinging together. I've never had the opportunity to get a close look at a swarm, interesting and spectacular. In the warm sunny afternoon there are bees buzzing off and back continuously. The new arrivals bury themselves into the body of the swarm. Presumably the scouts are searching for a suitable site. I understand they do this when the hive gets over full, so a group of them charge off to colonise a new spot. The bee industry would tell us that they have no chance against varroa mite on their own. These guys are trying it on.