Above photo credit to Val Wright
Q: I purchased a screened bottom board last year to help with a mite count, but I never got around to putting it in my hive. Recently I have been reading several posts on how beneficial it is to use in the hot summer months for additional air circulation. I just wanted to know what your thoughts are on this. The weather is going to be very hot this weekend, would you recommended replacing the solid bottom board with the screened bottom board and leaving it for the rest of the summer or is it something I should only use for mite counting and control in the spring and fall?
Happy Bee Keeping
A: The topic of screened bottom boards is one of those beekeeping issues that beekeepers disagree about. I can tell you our research-based opinion.
We try to mimic bees’ natural hives as much as possible. Their natural cavity is entirely enclosed, like in a hollow log or rock crevice, without an open bottom. Certain species of bees in tropical climates will have exposed comb, but that is not seen in temperate climates.
Bees’ preference is to use propolis to fill up any cracks in a hive. They seal all access except for their entrance(s). This gives us insight into how tight the bees would prefer their colony to be. We’ve never seen bees propolize the entire screened bottom board, but imagine they would if they could.
Honeybees collect water and place it on top bars of the frames. They use the evaporation of that water to cool the hive and control the humidity and temperature. With a wide open bottom, bees can’t do this. In Utah, it gets very hot in summertime during the day, but temperatures can drop 30 degrees at night. Bees need the brood chamber to stay in the mid-90’s for the brood to develop. If it gets outside this range, bees need to work to heat/cool their brood nest and bees expend extra energy that could be used for productivity. With an open bottom, bees have a difficult time regulating hot or cold temperatures. If it is 110 degrees F, then it’s 110 F inside the hive too. And at night, when it drops to 70 degrees, it will be 70 in the hive too.
Some people use the screened bottom board as part of their mite treatment plan. Mites naturally drop off of bees onto the floor of the hive, and then crawl back onto other bees and into the brood nest. If there is a screened bottom board in place, mites can drop through the screen and out of the hive. This can eliminate 10-20% of the mites in a hive. However, mites reproduce at much higher rates and this method is not very effective to eliminate them. It can be part of an overall natural mite treatment plan and work along with other treatment options. However, it is our opinion that the risk of chilling brood outweighs the mite treatment benefits from screened bottom boards, which only eliminate 10-20% of mites.
A good resource for mite treatment options is Honeybee Diseases and Pests from the University of Minnesota Extension Bee Lab. They have students researching treatment methods for mites, including screened bottom boards. We trust this manual because they recommend several treatment methods and harsh chemicals only as a last resort.
Some beekeepers use a screened bottom board to track mite levels. Instead of this, we recommend using a powdered sugar roll test
both spring and fall. The linked post includes a list of supplies, video demonstrations, simple calculations, and some treatment decision examples.
Screened bottom boards can also be expensive. Today at Mann Lake, a screened bottom board sells for $28. We sell solid bottom boards for $11. This can add up over 100 hives. Because the screen can chill brood in the winter (even sometimes with the insert in place), beekeepers may need to purchase both types of bottom board, and store the screened bottom over the winter. With our own bees, we avoid storing extra equipment wherever possible.
We’ve seen new beekeepers accidentally kill their hive from misuse of screened bottom boards. Some forget to put the insert in their screened bottom board going into winter. When they open the hives in spring, they find a cluster of frozen, dead bees. It is very sad when this happens! When I start to worry that bees are getting too hot, I like to think about the areas of the world that have lots of bugs (like India or Louisiana or Arizona). Insects thrive in very hot temperatures.
Our conclusion is that screened bottom boards are more gadgety than bee science. They can be useful on occasion as part of IPM strategy rather than everyday use. Even then, the 10-20% isn’t justified. We recommend and use solid bottom boards for honeybees.