Screened Bottom Boards vs Solid Bottom Boards

There are a lot of pros, and a few cons to screened bottom boards. In general, both screened or solid can work, and you won’t hurt your bees no matter which you choose. Bees in the wild live in spaces where there is ventilation under them, no ventilation, wide open, to completely closed. They are great at adapting. But, to help you make the decision as a beekeeper, here are some pros and cons of each style:

Screened Bottom Board Pros:

1. Keeps bees cooler during transportation. If you are buying or moving bees, having a screened bottom board dramatically increases the fresh air moving into the hive. Especially if you are moving hives during a warm day, or long distances, they help tremendously. 
2. Helps kill varroa mites. It’s important to note that a screened bottom board alone won’t control varroa mite populations, but it does help! When mites fall off bees in the hive they will fall through the screen, onto the ground, and die. 
3. Summertime ventilation. Strong hives are able to keep their hive vented by fanning even if they just have a normal solid bottom board. Where the screened bottom board helps primarily is on weaker hives less than 1 box full of bees. They are not always able to keep the hive as cool as it needs to be, thus a screened bottom board helps. There are some studies which have shown a slight increase in brood production for hives which have screened bottom boards. 
4. Repelling Small Hive Beetles. Like varroa, a screened bottom board won’t eliminate SHBs, but they hate light and ventilation. Thus, there tend to be a few less SHBs in hives with screened bottom boards. 

Screened Bottom Board Cons:

1. Strong hive ventilation disruption. During the summer screened bottom boards can make it slightly harder for strong hives to maintain the desired airflow throughout the hive. This is thought to be outweighed by the additional ventilation provided by the screened bottom. However, except for during transportation, strong hives seem to do fine with or without them when it comes to summer ventilation. 
2. Necessity of closing up the screen for certain mite treatments. When using any mite treatments that need to fumigate, like oxalic acid vapor, formic acid, apiguard, etc, you have to temporarily close the screened portion of the bottom board. This can be done by inserting a thin piece of poster-board or cardboard over the screen. 
3. Cost. Screened bottom boards are a bit more expensive to purchase or make. 
4. Winter considerations. During the winter months, it is not necessary to close the screened bottom board if you are in the southern half of the USA. If you are in the northern half, it is advised.

Overall, I believe screened bottom boards are a great tool to use as a beekeeper and the pros generally outweigh the cons. However, it is not a critical tool and bees tend to thrive when either is used.