An unfinished wood block with holes on each side, angled up, with a center wider hole that opens to a mason jar. The unfinished wood is the bait. Don’t paint or stain it. They can get in but can’t get out. They just die in there in a few hours.
This shows how to make the traps.
https://www.wikihow.com/Build-a-Carpenter-Bee-Trap
We have several hung, usually near where we see them. The first year we caught about 50, and the next year half that, and then the next year half that. Now we only get a couple in each year.
I bought our first one, and our neighbor made some more from that design. So we have 4 or 5 traps all around the house. They’ve helped A LOT.
It looks like one could easily modify the design to work with clear soda bottles and sections of downed branches about 4” in diameter. The former are easy to come by (including in our ditch every few days!) and the latter we have plenty of - some slightly older so the wood is slightly “punky” but not rotted.*
*The one thing that surprised me in the article @ the link was the recommendation of using treated wood. I’ve not seen the carpenter bees go into pressure treated wood unless it was pretty old. Of course, in this case they are not actually chewing into it.
We got quite a “blow” (storms’ winds) this evening, so there will likely be even more wood down in the woodlot @ the east end of our property. Luckily, I don’t think we got any real damage. I’ll do a more thorough (but chilly!) walk-around in the morning.
Thanks!