Your captives are letting off pheromones to signal their distress at being incarcerated in a Henry. More of their mates will rock up to assist in their repatriation. They might be pissed off at being unable to achieve said goal.
If you are too wary to release them in the dark, take Henry outside, remove your bung, and retreat indoors. They may or may not be intelligent enough to find their way out via the hose, but if they have a similar IQ to their wasp cousins, who can't recognise a wide open window, I fear you may have to assist their escape in the morning.