How to handle bees which have taken residence in holes on the underside of our deck and routinely swarm the table space area on top of the deck outside kitchen sliding doors without presence of food. Often see a trail of wood dust suggesting the boring into the underside of the deck.
It sounds like you have correctly identified your Carpenter Bees.
They are native and non-aggressive and are draw to wood that has not been painted, stained, etc.
Here is our page about them, including control if need be: