Carpenter bee traps are not an original idea, but in searching for an instructable, I discovered no one had posted plans. Since I needed to make some traps I thought an instructable was in order. There are many designs and you can google for images to see the variety. Most of them are pretty close to this design.
Step 1: The trap is set
Step 2: Building the box
The third and fourth pieces serve as the other sides. They are made from 3" wide wood and it's easiest to just rip some 3" wide boards before you start. I don't have the exact measurements for the length because it will depend on how tall you are making your box. Instead, take one of the trapezoid pieces and use it to mark the length of the side pieces. Your marks will be at angles oriented in the same direction. These are also 10° cuts on your miter saw and make the top and bottom of the trap flat. Assemble your box with some wood glue and nails. Don't get your nails too close to the top if you plan to slope the roof (read on).
Picture 2 - To slope the roof a bit I tipped my miter saw 10°-15° and cut the top as far as possible. I finished the cut with a hand saw. When assembling your box make sure to keep the nails an 1" or so from the top so you don't saw them.
Picture 3 - Drill a 1/2" hole angled upward in each side near the top. The bees prefer to climb up into a hole and it also makes it harder to find the hole when they want to leave.
Step 3: Making the bottom of the box
Once your hole is cut slide the bottle through, cut off the bottle and make some tabs with a sharp knife. Staple the bottle tabs to the wood and place the block inside the trap box. Picture 5 shows what the inside of the trap looks like from the top. When the bees enter the box, the plastic bottle is the obvious exit as it is the only source of light in the box. The bees fly down and enter a second plastic bottle which we will prepare next.
Step 4: Finishing the bottles
Update: UncleSam created an instructable on how to connect the 2 caps using a 1/2" grommet. Very nice permanent solution.