There is mid 17th century bee-keepers' saying: 'A swarm in May is worth a load of hay, a swarm in June is worth a silver spoon, but a swarm in July is not worth a fly' - meaning that the later in the year it is, the less time there will be for bees to collect pollen from flowers in blossom.
May in west Oxfordshire saw the start of swarm season and we had four swarms arrive in the garden in little over a week. Honey bees swarm in order to set up new colonies, leaving with their queen and searching out new territory. Scout bees will have gone out first to look for suitable places to settle. If they find somewhere, they'll wait for warm dry weather and then set off from late morning to about 4pm. Often they'll stop off for a rest, a tall tree being a favoured spot.
There is a tall tree in the garden here, a mature Magnolia soulangeana, and last year it attracted one swarm that we know of. There could have been more since swarms settle quickly and you might not even know they were there unless you'd seen them arrive. The bees' main aim is to protect the queen so they don't want draw any attention to themselves which could attract predators. Unless they've been out of the hive for several days, they'll be full of food, having eaten as much as they can before leaving, and will remain calm.
This May we happened to be at home for a week so were able to see what was happening. The first three swarms arrived on Monday, Wednesday and Friday – the first we caught and hived, but the others were too high to reach and went on their way after a few hours. Why so many swarms? It's likely that the during the time the bees were in the tree they left Nasonov pheromones, which signal 'We're here' to the rest of the swarm. Others bees smell it and choose to stop off in that tree themselves.
Swarms arriving every other day started to feel a bit surreal and we fully expected another one to turn up at the weekend. This gave us the opportunity to test out an idea we'd seen, a swarm box. This is a box designed to attract swarms and is used in Europe and the US by beekeepers wanting to increase their number of colonies. The idea is that rather than cutting branches from a tree to remove the swarm they just move into the box on their own. The tree in the garden was already attracting swarms, so it could work. There was scrap wood about and box was quickly made up (plans here) and set in place, high up in the Magnolia.
We weren't especially surprised when, within an hour of the box being fixed into the tree, scout bees had started to investigate. Small groups arrived and crawled over the surface, then they went inside and had a good look around. Two days later they moved in and set up hive activities. There you have it. If you're after a colony of bees to give a home to and take care of, this could be worth a try.