Imagine this scenario: As spring leans towards the beginning of summer your hive inspections show you that your best overwintered hives are getting super-charged. It's gratifying to think that all your efforts to care for them have turned out so well. But you know that it also means you have an increased chance that the hives will swarm. It's a cruel irony, but one you must deal with, somehow.
Many things can be done to try and forestall a swarm (careful frame management, keeping young queens, with lots of room in drawn combs to lay, etc.), but your hives may still be headed for trouble, despite every tactic you've tried. However, you've got an ace up your sleeve: You can split the colony.
Splitting is the commonly-recommended solution, but it's not without its secondary problems. Two split hives generally don't produce as much honey as a single, large colony. Splitting isn't always successful in stopping the swarm, especially if the hive is very close to swarming. Some kinds of splits require you to move one part of the split to another location in order to work well.
And all of them share the same problem: once you've made the split, you can't go back and keep adjusting the division of the bees between the two parts afterward, even though the population in each part is changing every day.
Fortunately, there is a tool which allows you to have it both ways: splitting your hive to stop a swarm (even quite late in the progress towards a swarm) and still allowing you to use the bees' own biology to maintain stable and honey-productive units after the split.
Double screen boards: A reliable way to stop swarms
The double screen board was invented, and first described, by an English beekeeper named Leonard Snelgrove in 1934. This board allows you to make a vertical split with both parts remaining in a single stack after the split. But Snelgrove's invention goes beyond just keeping the two parts together on the same base. The double screen board has three sets of paired doors that allow some of the bees to be shifted between the two units after the split in order to maintain a non-swarmy assortment of the various age-classes of bees in each part of the split.
To understand the importance of this, you need to think about what types of bees would make up a swarm. The “old” queen, of course, leaves. But she takes mostly younger bees with her, not older foragers who would only have a short time left to live. The swarm needs mostly younger bees, with their longer potential life spans and better wax-making potential. To have any hope of success, the swarm must get the new colony established with drawn combs so the queen can begin to lay eggs as quickly as possible. (Bee swarming behavior evolved long before beekeepers and their swarm traps were in the picture.)
What Snelgrove accurately observed was that a hive on the path to swarming could be halted if the bee population's age-assortment could be altered. In other words, if the queen needs young bees in order to swarm, if you separate her from most of the younger bees in the colony, the swarm process will be naturally arrested. And most importantly, if you also had a way to continuously keep re-adjusting that age-class assortment as colony's brood kept hatching out, you could keep the swarm process halted until the swarm urge had passed and the colony had settled down for the year to make honey. A double screen board does exactly that.
Anatomy of a double screen board
Let's look at the board: The most obvious feature is that there is a large screened area in the middle. This allows both parts of the split to share a common hive scent, even though they are divided. This common scent permits bees from one part to move to the other without being identified as “strangers” and being rejected.
If you look closely, the screened area isn't just one layer of screen. There are two screens (that's the “double screen” part of the name). The distance between the screens is far enough apart so that bees from the part with the queen can't reach through and pass along any queen pheromones. The lack of queen pheromones is what prompts the queen-less part of the split to immediately begin emergency queen cells, despite the shared scent.
And, then there are the paired doors. These doors are what make the board seem tricky to use, but they're quite simple. Here's how they work: when bees from one part have oriented on an entrance, they can be redirected to the other part if their accustomed door is closed, and the door leading to other part(which is immediately below it) is opened. The shared hive scent ensures they will be readily accepted. Harnessing this innate orientation-to-a-particular entrance behavior allows the beekeeper to keep the ages in both parts of the splits balanced. This keeps the swarm-potential low, as well as maintaining a steady level of foragers to work a strong nectar flow. This eliminates the population bust that is the usual consequence of a split when there is an interruption of egg laying.
Now that you know how the board works, let's work through its use in two familiar situations:
- A hive that looks strongly as though it might swarm soon, but there are no visible queen cells. This would be a pre-emptive split.
- A hive that has already begun to make queen cells, but none are fully mature or capped. This would be a swarm-stopping split.
The instructions for these two types of splits are detailed, because the process seems quite complicated at first. (Those tricky doors!) But if you understand the concept of what you're trying to do, it comes into focus easily. I have tried to include the “why” along with the “what to do” steps. This is my version, based on an excellent paper by Wally B. Shaw, "The Many Uses of a Snelgrove Board."I highly recommend you read it for a more in-depth description, including some excellent tips on what to do if you can't find the queen when needed for a particular step in this process. A “Snelgrove Board” by the way, is just the common name in the UK for what we call a double screen board.
I confess that I, too, was daunted by the description of this process at first. I had someone out in the bee yard reading me the instructions in Shaw's paper during my first attempt. Only my desperation to try and avert a swarm kept me at it. To my surprise and delight, it worked extremely well and I have used it many times since with complete success. Now I routinely teach it to my second-year students because it is both easy and reliable. Swarming is such an annoying end to a year's efforts to keep a colony healthy and strong, that I think it's worth the trouble to learn an effective way to stop it.
Click here, to read how to use a double screen board to do a pre-emptive split in a hive without queen cells or how to use a double screen board to do a swarm-stopping split in a hive that already has queen cells started.
