Do hundreds of bees need to keep warm in early summer?

Generally speaking, it is not necessary.

The heat preservation of beehives should start around the light snow solar term, with the temperature below 0℃ at night and around 5℃ during the day. It is most appropriate to keep the bees warm at this time. The best state of wintering is that bees gather together and stay quietly in the hive. As long as the weather is fine, bees can occasionally leave the nest to excrete.