This activity is called bee festooning. Festooning is seen most often when bees are constructing new comb or repairing old comb. The bees hang together between the frames that they are building, connected to each other by their legs. In a festoon the bees hang together in a single line, only one level deep – which is different than a typical “clump” of bees, which is many layers of bees deep. It appears that festooning bees are creating some sort of scaffolding from which to do their important construction work.
Festooning behaviour is clearly associated with wax production and comb building. Some believe that the purpose is mainly to scaffold, others believe that the festoon is a method of measuring distance between combs. The Precise distance between combs is very important to honeybees. Others believe that it somehow is responsible for starting or increasing the flow of beeswax. Whatever the reason, the festoon is fun and fascinating to watch, and is a sure sign that the bees are now in full “construction mode.”