Beehive Bearding - it's not cause for concern or an indication of swarming. It's how the bees regulate the temperature inside the hive keeping it from getting too warm. It's also generally a good indication of a strong/healthy colony.
European bee houses (the hives stay inside the houses and open at the back) – and a US and UK bee house. Images of the wonderful painted hives, and a look into how the eastern European hives… - Bee House Gardens