What action do guard bees take when they detect an intruder?

When guard bees detect an intruder, they typically respond by marking the site with a pheromone. This pheromone serves as an alarm signal, alerting other bees in the colony to the presence of a potential threat. By marking the area, the guard bees effectively communicate the location of the intruder, which helps activate the colony’s defensive response. This coordinated effort is crucial for the survival of the hive, as it allows more worker bees to gather and mobilize against the intruder.

While some guard bees may escalate the situation by stinging to physically repel the intruder, the initial action often involves marking the intruder's presence. This pheromone signal is important for directing a larger response, making it a key component of the hive's defense mechanism. The option that suggests guard bees retreating to the hive does not align with their role in protecting the colony, while calling other bees for help may occur after the pheromone is released but is not the primary initial action.