What is it?
A double-screen board is about 1-inch deep with an opening in the center. The center opening is covered with screens on both sides so that bees on one side of the board cannot contact bees on the other side of the board. It often comes with openings in the rim that can be toggled open or closed. These are in pairs (an upper and a lower) on each side of the board. Some boards have a total of eight openings, some have just six.
This piece of equipment is also known as a Snelgrove board, after L. E. Snelgrove who used it to control swarming. His method—a bit complex—is a subject for another day. However, there are many other uses for his clever invention.
How is it used?
1. For queen introduction
1.1 When introducing a new queen to an especially strong hive, pull a frame or two of emerging brood and a frame of honey out of the brood chamber and replace them with empty comb or foundation. Remove the old queen.
1.2 Place the double-screen board on top of the chamber
1.3 Place another box containing the emerging brood, honey, and the caged queen on top.
1.4 Open one of the back entrances so the newly emerged bees can come and go.
1.5 After a few days, release the queen in the upper box.
What is the benefit? Newly emerging bees will be more accepting of a new queen than the old foraging bees. After a few more days you can close the back entrance and open the front two. This way the bees will slowly start to mix. After a few more days you can remove the double-screen board completely.
2. For combining two hives
2.1 Place the double-screen board between a queenright and a queenless colony before combining to allow them to adjust to the new scent.
2.2 Open an entrance to the top box on the back.
2.3 After a few days, close the back entrance and open the two front entrances to allow the bees to mingle. Later, remove the double-screen altogether.
What is the benefit? It allows the scent of the queen to circulate throughout the boxes before the bees can come in contact with each other.
3. For over-wintering a weak hive
3.1 Place a double-screen board above the brood box of a strong hive and then put a weak hive above it.
3.2 Open one of the entrances so that the bees from the weak hive can come and go. This entrance should be on a different side than the entrance for the lower (stronger) hive.
What is the benefit? In this way, the weak hive gains the benefit of the warmth from the hive below, but the hives remain separate. It improves the chances of winter survival for a weak hive that might have trouble keeping warm.
4. For moving a hive in hot weather
4.1 If your bees must be confined to the hive in hot weather, fasten the double-screen board on the top of the hive in place of a solid cover. Nails or screws can be used, but screws do less damage.
4.2 Make sure all the toggle entrance are closed.
What is the benefit? This is basically the same as a “moving screen” which provides extra ventilation to bees that have limited ways to keep the hive cool.