Bee boxes generally come with one side planed smooth, and the other left rough. When assembling boxes, you will need to decide weather to put the rough side of the wood on the inside or outside of the box. We recommend putting the rough side on the inside of the box. Here's why.
Honeybees will note any imperfections in the wood and fill them with propolis. Propolis is essentially the bees’ immune system.* It significantly helps fight off disease (bacteria, fungus, virus) and is a sticky, glue-like substance collected from some budding plants. Having the rough side on the interior makes bees add more propolis than they would add to the smooth side.
Research from the Minnesota Bee Lab shows increased disease resistance in hives where the box was coated with a propolis solution. Also, in preliminary tests, even the HIV virus couldn’t live in a petri dish with a propolis-alcohol solution.
However, there IS an advantage to putting the rough side OUT if will paint your boxes. Paint sticks better to the rough-planed side of the box.
But it seems to us that the advantages to bee health outweighs painting and we put the rough side on the inside.
*(Okay, so technically an immune system is the one that remembers infectious diseases a body has been exposed to in the past and carries antibodies to fight off the disease-causing organisms. Insects don’t have an immune system like this at all.)