Oppure hanno deciso che l'ombrello sarebbe stato una casa abbastanza buona a causa della mancanza di opzioni in un ambiente urbano o stavano solo aspettando lì mentre le api scout erano fuori a cercare un nuovo sito di alveare.

Honeybees produce a swarm to propergate themselves. It's a very common process, all honeybees you see exist because their hive was created by swarming.

Think of a colony of bees as one super-organism. An individual bee cannot survive on its own, anymore than one of our cells can survive on its own.

What to do About a Bee Swarm - What is a Swarm?