I have been out on three "swarm calls" in the past week or two here in Middle Tennessee. Since I (like most of the nation) have suffered heavy colony losses this past year, I am ecstatic when asked to go gather up these swarms. I love, love, love, collecting swarms!
Swarms usually occur on the first sunny spring day after the bees have been cooped up during rainy weather. As a beekeeper, I've always tried to observe, learn from, and work with the bees' natural swarming tendencies. My goal is not to thwart this natural process, but to work with the bees--a winning endeavor for both of us.
I have learned that bees begin preparing for swarming almost as soon as the queen resumes laying eggs in late winter/early spring. If a colony is strong and has plenty of honey to get through the winter, it will begin swarm preparation at the time of the first available pollen. In my area, that means the availability of elm and maple pollen as early as February.
Beginning in February, I will watch for the first warm, but temporary, break in the weather--when temperatures approach 70 degrees. That's when I check my hives. If the bees have moved up into the second deep box, leaving the bottom one empty, I will reverse the boxes--so they have room to move up. This is tricky, depending on the weather. If the bees are still divided between the two boxes, you do not want to split up the cluster and expose the brood to chilling temperatures. If all of the bees have moved up into the top deep, you can safely reverse the hive boxes.
The second part of this late winter/early spring management is to break up the honey dome. I always leave one shallow super of honey atop the two deep boxes. If the bees have eaten all of this reserve, I will give them frames of honey from other hives or from what I have saved in my freezer. If this box is still full, it becomes a "honey dome," and makes the bees think they are running out of room. They prepare to swarm--they have plenty of honey and nowhere to store new honey. Breaking up this honey dome is key to preventing swarming later in the season.
Breaking up the honey dome involves a procedure called "checker boarding." Every other frame of honey is removed from the top super and replaced with empty comb or foundation. A second shallow box is added above to house the frames removed from below, alternated with empty comb or foundation--thus the term "checker boarding." You have relieved congestion,and the bees have room to expand within the hive. An added bonus is that you know this hive will most likely produce two or more supers of honey for you once the nectar flow begins.
For many hives in these times of travail for the bees, these manipulations will be enough. The bees have room to work and expand, and you get to keep your bees and your honey harvest. For very strong hives, as in days gone by, you will need to "artificially" swarm them later in the season--take a nucleus hive or a split to relieve congestion. The best timing for this is at the beginning of or just after the spring bloom or nectar flow--just before the sisters can do it for themselves! Take three or four frames of bees, eggs (less than 3 days old), pollen, and honey and move them into a new hive. Seven times out of 10, they will make a new queen and build up a new hive. The main colony will think they have swarmed and will settle into making honey, and you will have a brand new colony as well as the main colony and it's honey crop. Everybody wins!