The bees in the green box are using 6 frames which is now too small for the queen to lay more eggs and store honey - look at the fresh white honeycomb on top of the frames a sure sign they need to upsize. They are being moved across to the bigger 11 frame hive on the left which is now in the place the green hive was so the bees will have no trouble finding the entrance again.
Picked up another swarm today which had gathered on the mesh of a fruit cage:
A combination of a quick shake and a then a brush to remove the remaining bees and sweep them into a box to join their fallen comrades. Now safely re-hived elsewhere.