They can Hide Inside your Vents
Bees are very picky about where they build their nests, and vents are the perfect location. They are hard to spot and provide everything the bees need. Bumble bees especially like to nest in places humans wouldn’t think of, but they will do whatever it takes to ensure their success. Luckily, they don’t bite or damage property.
You may have to host some winged guests if your vent goes somewhere bees are known to travel. If the bees can get back out of the vent, they will likely leave the nest and go into the garden to look for flowers. It might be faster for them to go through your room instead.