Bees form a mass in winter and work their wing muscles to keep themselves warm, rotating bees between inside and surface so none gets too cold for too long. So

Bees form a mass in winter and work their wing muscles to keep themselves warm, rotating bees between inside and surface so none gets too cold for too long. So they did have a base behavior from which the surround-and-cook behavior could evolve. When I first heard about the hornet defense I wondered how on Earth the bees could've come up with that. But if they already clumped up for warmth it's a lot more scrutable.