In spite of our best efforts an occasional swarm will get by us and our bees will leave the nest. Once this has happened we have a couple of options available to us. Chances are pretty good that we can call it quits for honey production from the hive that the swarm came from. This is because of the timing of the nectar flow and the fact that we have no late flow of nectar to take advantage of like they do in other areas of the country. Dividing the hive during the nectar flow places many of the foraging bees back into the housekeeping role and they act as consumers rather than producers. Here are some options that you might try to use in that portion of beekeeping that we deal with swarms.
First of all you must catch the swarm. Remember that you are in a time limit. As you get ready to capture the swarm the scout bees are busy checking out future homes for the new hive. Remember that the spot that the swarm settles is just a resting place for the queen to hang out till the new home has been approved by enough bees to make the final move.
Once you have gained access to the swarm you can temporarily put it into a box. If you are able to clip the branch that the swarm was resting on that is really good and you can place the swarm in the box in a relatively undisturbed condition. If you are really lucky you can use a deep super for your swarm box and the lay the swarm directly on the top of the frames. I have had bees move right down into the box with a very light puff of make to the top of the swarm. If you can't take the branch with the swarm then shaking the swarm into your box is the next best thing. A good sharp shake to the resting place can knock the bees off their perch, so don't be timid about your shake. The object is to get the queen into the box. If you miss her, the bees won't stay. Don't be surprised if the some of the bees that are flying around land where the swarm used to be because it still smells like the queen is there. If your box is still under the swarm site you might pull the lid nd give another sharp shake. You will never get all the bees and very likely the bees that are left out of the process will wind up back in the same hive that they came from. So which hive was that? I have never tried it but if you wanted to I suppose you could mark a number of the bees that remain and see where they end up during your next hive checks. Logically the first thing that you would look for is the hive that has fewer bees in it but it may not be obvious which one it is.
The biggest question of what to do with the bees once you have caught them depends on what goals you have with your apiary. If you have intentions of expanding your operation then it might be a good idea to put them to work with drawing comb for next year's operation. When bees swarm, they really go into the wax production mode and can be really useful for this purpose. Put some feeders on them and let them work. You will be surprised how quickly they can draw comb. Remember the basic principles of drawing comb and try to set things up for maximum production. Give lots of food and keep the space down to a minimum. When they finish drawing a super of comb don't just add another super but instead pull out some finished fames and replace them with some foundation.
The other option is to try to combine the bees with another hive or perhaps even with the original hive. This will entail setting up the hive and running it as a two- queen system with an excluder between the two hives. Don't simply put the bees back into the hive they came out of, it won't work. The bees left that hive for a reason and they won't stay there if you just dump them back in. Here is one common method of combining a hive with another one. Place a screen between the hives so that the bees can't mingle with each other but the hive can have the same airflow and smells for a few days. Reduce the entrances of both hives so that there is a small enough entrance for the bees to defend for robbing behavior. Remove the screen and replace it with a queen excluder over which you have placed a couple of sheets of newspaper. Make a few slices in the newspaper to allow the bees to chew through the barrier and intermix slowly. At this point I would not mess with the hive for at least a week to give the bees a chance to adapt to the new queen.
The problem with this second approach to the placement of the swarm is that there is the possibility that one or both of the queens could be lost in the process. If the hive that you are combining is going back onto the original hive and you can find the new queen, it may be a thought to get rid of her since she is unlikely to become fertile and reproductive until the second half of the flow, or even after the flow. This is bad timing unless you have intentions of wintering your bees. In this case you can skip the excluder and allow the bees to become one larger hive. They likely needed another hive body after all.