Bees swarming is a natural thing and although beekeepers can breed from their less swarmy bees, not all do. However colonies will swarm, even with the best bred bee. I was called to look at some bees by a gardener who found bees flying out of a concrete box on the grass which was hiding some gas pipes. Here’s a couple of pictures from what is generally called a “cut out” where the colony had comb and brood already in the cavity they made their home. What seems to work is putting existing comb into frames and fixing them in with masking tape. It sounds easy but it can be a bit awkward to do. If the bees are well-behaved, as these ones were, it helps! After a couple of weeks the tape has been chewed through, by which time the comb has been well and truly fixed to the frame. Simples!