We had one heck of a problem with carpenter bees some years back on our cedar house way out in the woods. We tried everything imaginable including the various expensive and toxic professional sprays done by exterminators and caulks, caulks, caulks. You name it. We tried it. The bees chuckled at our feeble efforts and kept on buzzing/boring/swarming/krapping/occasionally stinging.
Even got out the badminton rackets and started whacking those little buggers one and two at a time... sometimes many hundreds per day. Tennis elbow anyone?
I thought I was making real headway with the racket until I observed about 60 bees pour out of a single hole one day... and we had thousands of holes under the eaves mostly... but in the siding too. Very discouraging.. and the bee poop and detritus was overwhelming.
On a hot summer day, we might have swarms of bees buzzing everywhere. We thought about replacing the beautiful siding.... and then the answer.
Aluminum screen wire, bronze in color to blend in with the siding, carefully and painstakingly tacked seamlessly under the eaves with a staple gun. Nearly invisible. The bees could not enter or leave and they couldn't eat thru the wire.
Anytime we found an active nest in the siding itself, we tacked a small 4 in by 4 in patch right over the hole and checked it from time to time to make sure that the bees inside had not bored a new exit around the patch... and sometimes they did. Tricky little devils. Another patch in place. No more active nests. The bees that hatched out after the screen wire was in place died painful deaths trying to get out from underneath the barrier and I rejoiced at their pitiful plights, feeling ever so smug!!!
Victory over insects! Those buggers can really propagate exponentially!
At some point, I may try to remove the patches and restain and recaulk the previously infected areas, knowing that the bees are no longer inside the siding and eaves propagating the species.
The problem only gets worse. Go after them early and aggressively using a barrier approach.
Otherwise, if ignored or tolerated, they come back year after year in larger and larger numbers.
It took us about 10 years to realize that we had a serious problem and about another 5 years to find the solution.
Now not a single carpenter bee around this year.... well maybe one or two!