When it gets really hot, bees will sometimes “beard” the hive. One hive in particular used to do this all the time. It had pretty good ventilation (screened bottom board, propped top cover) but they often did this all night.
Many bees come and go from the hive but many remain doing other work. Some of these bees are standing on the landing board fanning their wings to cause a draft through the hive. They will sometimes bring a drop of water back and fan over the water to maintain the proper temperature.