Why do bees collect on the bottom board?
Brood nest temperatures remain fairly constant throughout the year at 93°-96° F (34-35° C.) But while a colony in late winter may consist of only 10,000 bees, a summer colony averages about 50,000 beesand in some cases the summer population may reach 70,000+. With all those bees in the hive, the brood nest has to be cooled to keep it at the ideal bee-rearing temperature.
As temperatures increase in spring and early summer, it is not unusual to see throngs of bees sitting on the bottom board near the entrance to the hive. Even early in the morning after a cold night, they may be all lined up, looking like they are about to swarm.
However, congregating at the entrance is normal behavior for this time of year. Think of it this way:
Even a small cluster in the dead of winter manages to keep the brood nest warm. Individual bees take turns pressing their bodies against the brood and, by doing so, the baby bees are incubated at a cozy ninety-some degrees Fahrenheit.
But as the outside temperature gets warmer, so does the inside temperature. In addition, the number of hive occupants rises dramatically. So, instead of having a heating problem, the hive now has a cooling problem. Too many bee bodies sitting on the brood may make the brood too hot for optimum development.
In addition, the vast number of bees in the colony restricts the air flow through the hive. This occurs at the same time that the bees are trying to dry down the nectar and turn it into honey.
In response to these problems, the bees congregate in different places. They begin by sitting on the bottom board. As temperatures rise even more, the bees may “beard” on the outside walls of the hive, or hang in festoons from the landing board. Think of sitting on the front porch to stay cool on a hot summer’s daysame thing.
Follower boards and slatted racks can both provide additional congregation areasplaces where the bees can sit without overheating the brood or restricting air flow through the hive. You can also help by providing screened bottom boards, screened inner covers, and upper entrancesall of which increase air flow through the hive.
I am probably guilty of over anthropomorphizing bees, but it is one of the easiest ways to figure out what they are doing and why. We need to stay warm in winter, and so do they. We need to stay cool in summer, and so do they. When we have excess moisture in our homes, we try to remove itand so do they.
Remember, though, that even if the air feels chilly to you, the bees have huge numbers of individuals in their homes that we don’t have. So even a modest increase in the outside temperature can have a significant impact on the inside temperature, and the bees react accordingly.