How to Customize Your Hive With a Screened Inner Cover and Imirie Shim
Improving Summertime Beehive Ventilation
Just as you can alter the entrance to your Langstroth beehive, you can also alter the top. Two pieces of optional equipment to consider are a screened inner cover and an Imirie shim. Both can be used to improve summertime ventilation and increase honey production.
What is a Screened Inner Cover?
A screened inner cover is used to replace a regular inner cover during the warm months. It is simply a frame in the same dimensions as your Langstroth beehive, but the center is made of eighth-inch hardware cloth instead of wood. The two short sides of the screen have risers that hold the telescoping lid about an inch above the screen, allowing air to escape from the two long sides, greatly improves beehive ventilation, and helps to keep the honey bees cool.
The screen allows warm air and water vapor to flow easily out of the top of the hive, but at the same time, the screen is small enough to keep out most pests and predators including wax moths, flies, wasps, and other honey bees. The telescoping lid fits down over the screen, which keeps out the rain and the wind.
Screened inner covers also offer the unexpected benefit of acting like a window into the hive. I can lift the telescoping cover and see down between the frames without disturbing the bees or having them fly out at me. Sometimes a quick peek is all you need, and screened inner covers are perfect for that.
How Does a Screened Inner Cover Help the Bees?
Not only does good ventilation keep your honey bees cool, it can also increase your honey yield. Nectar is about 80 percent water, but honey is only about 18 percent water. To get rid of all that extra water, bees add enzymes and then fan their wings furiously. It takes much time and energy to fan away all that water, especially if there is no place for the warm moist air to go. If the moisture is locked inside the hive, hours of fanning will make little difference. But if the moist air is allowed to escape through the screened inner cover, honey can be cured quickly and efficiently.
Your choice to use a screened inner cover will have a lot to do with your local climate. In arid, desert areas with lots of dry wind, they are probably not necessary. In areas of high humidity or places with long, unremitting rainy seasons, they can make a world of difference. The main point to remember is all beekeeping is local and, like children, every colony is different from all the others. A screened inner cover is easy to make (https://honeybeesuite.com/how-to-make-a-screened-inner-cover/) or inexpensive to buy, so give one a try and see if it works for you.
The Benefits of an Imirie Shim
In addition to a screened inner cover, you can also add an Imirie shim to the top portion of your hive. An Imirie shim is simply a rectangular frame of wood, about 3/4 of an inch high, with an entrance hole cut into one end. The original designer, George Imirie, insisted that their only use was to provide upper entrances between honey supers, but thousands of beekeepers since then have found alternative uses for them.
Imirie Shims for Honey Production
Beekeepers who do not want to drill holes in their honey supers like to use Imirie shims between honey supers. Entrances in or near the honey supers are more efficient for honey-carrying bees because the bees do not have to travel from the main entrance up to the supers and then back down again. Instead, the foragers fly directly into an upper entrance and quickly deliver their nectar to a receiver bee who then deposits it in a honey cell. Not only is it quicker, but it saves wear and tear on the bees, especially those that would have to otherwise squeeze through a queen excluder.
Not only is nectar delivery quicker, but the openings provide better beehive ventilation for curing the honey. Similar to using a screened inner cover, upper entrances allow the warm moist air to escape easily, which makes fanning away the excess moisture easier to do. Most beekeepers who use the shims for upper entrances, add one honey super, a shim, then two honey supers, a shim, two more honey supers, then a third shim, and so forth. But other beekeepers like to place one above every super.
Imirie shims as spacers
Imirie shims can also be used as spacers. The extra 3/4-inch of space can be used to hold varroa mite treatments, pollen supplements, or thin sugar cakes. If I’m using the shim as a spacer, I sometimes wrap the entrance of the shim in duct tape to keep bees from using it. This is especially true during times of robbing by other bees or wasps. As handy as they are, however, Imirie shims should not be used between brood boxes. The bees need to keep the brood-rearing areas especially warm and compact, so extra space with or without an entrance should be avoided within the brood nest.
Imirie Shims in Winter
Upper entrances in winter are controversial — useful in some climates and detrimental in others. But for those who decide to use an upper entrance in winter, an Imirie shim does the job well. I use an Imirie shim just below a candy board for overwintering, and my bees use that entrance almost exclusively all winter long. It is small enough to keep out most pests, wind, and rain, yet it is easy for the bees to access on days when they want to take a quick cleansing flight. They can dart out and back quickly without having to travel down through the cold hive to get outside.
So what am I forgetting? Do you have still more uses for a screened inner cover or Imirie shim? Please let us know.