Venting the beehive
Do I need to vent the hive to keep them cool?
As long as the bees have an unobstructed hive entrance, they can do a wonderful job of air conditioning their hive.
They do that by gathering water and placing droplets in strategic locations throughout the hive.
Then bees throughout the hive arrange themselves so that by fanning their wings they set up a circulating current of air in the hive. They draw fresh air in, circulate it throughout the interior of the hive, and then expel the air.
As the air circulates, it passes over the droplets of water, and gradually evaporates them. The evaporating water cools the air, and lowers the temperature within the hive.
If you look closely at the hive entrance on a hot day, you can often see furiously fanning bees on one side of the entrance facing in one direction to draw air in, and bees facing the opposite direction on the other side of the entrance drawing air out.
Sometimes - for a very populous colony during the hot part of the summer, I'll create a temporary upper entrance just by slightly staggering the top super, as in the photo.
I feel that this not only makes it a bit easier for the bees to cool the hive, it also helps to ease congestion at the bottom entrance.
But many beekeepers just stick with only the bottom entrance, and the bees do fine.
If you have a strong colony, though, you do want to be sure that the entrance isn't restricted with an entrance reducer during the warm part of the season.