This easy trap will help control carpenter bees that threaten your home without the need for baits or poisons, and it will not attract or harm any other kind of bee or insect. The trap will not lure carpenter bees in from a great distance, but will trap those that are intent on damaging the protected structure. Wood-boring female carpenter bees enter the pre-made holes, then they become dessicated by the sun in the capture bottle. The first day this trap was installed, it caught the four bees shown in the photo.
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Step 1: Components
There is nothing special about the components and their dimensions. Feel free to substitute, though I would not use plywood for the sides of the box because its exposed glue might deter the bees.
Wood for box, solid, one inch thick, 4 inches wide, does not need to be weathered
Wood for box lid, I used a scrap of 1/4-inch thick marine plywood 4 and 3/8 inches square
4 drywall screws for attaching lid to box
wood glue for outdoor use, such as Titebond II, to assemble the wood box, or alternatively drywall screws
Rectangular plastic 500 ml Fiji bottled water bottle and its cap (WalMart). This is the only rectangular bottle I could find, and it is sturdier than most other water bottles.
Deer Park Aqua Pod 325 ml plastic bottled water bottle and its cap (grocery store).
Metal grommet for connecting the bottle caps together, sold as part of a kit for placing grommets in tarpaulins; alternatively, outdoor tape
Step 2: Make the Wood Box and Drill Entry Holes
The box is four pieces 4 inches high by 3 and 3/8-inches wide each joined using only wood glue and clamps. Connecting the pieces together in a spiral configuration allows all four pieces to be the same size. These dimensions will create an interior opening that will be a sliding fit with the Fiji bottle only if the wood is one inch thick. Wood of a different thickness can be used, but the width of the pieces would need to be adjusted to ensure that the interior square hole is 2 and 3/8 inches square, if the spiral assembly configuration is used. Drill a hole 1/2-inch diameter into the side of each wood piece, with the hole angled upward at about 45 degrees. Begin at about the halfway point, measured from top-to-bottom. Each hole should be placed so that it will end up in about the middle of the interior square, as measured from side-to-side. For my box, this means that the hole would be drilled about 2 inches from the bottom and 2 and 3/16-inches from the left edge of the wood piece that is facing the viewer in the photo. Mark the rim of the box that has the interior ends of the holes closest to it as the "top." You want the bees to travel upward as they crawl inward.
Step 3: Fit Plastic Bottle and Mark It for Holes
Cut the bottom off the Fiji bottle, and trim its length so it almost fills the box's interior hole. Put a match mark on one side of the bottle and on the same side of the box. Trace the holes on the inside of the bottle, then slide out the bottle and cut out the holes in the plastic. A pair of curved fingernail scissors works great.
Step 4: Prepare Lid for Box and Box for Lid
Mate the lid to the "top" rim of the wood box, match mark them both, mark and drill holes in the lid for screws, countersink the lid for screw heads. Drill pilot holes in the box for the screws, but do not attach the lid to the box yet.
Step 5: Attach Bottle in Box
Match up the match marks and slide the Fiji bottle into the wood box, with its threaded neck hanging out from the "bottom" rim of the wood box. Ensure that the holes in the plastic line up with the holes in the wood then attach the bottle into the box. I used an ordinary office stapler to place four staples, then tapped them flush with a small hammer.
Attach the lid to the "top" rim of the box using four screws. Do not use glue, in case the lid needs to be removed in future in order to replace the Fiji bottle.
Step 6: Connect Two Bottle Caps Together
The best way to connect the two bottle caps together is to use a metal grommet, as shown in https://www.instructables.com/id/Attach-Plastic-Bottle-Caps-for-Carpenter-Bee-Traps/. If you want to try some kind of outdoor tape instead, cut out the flat part of two caps and hold them together while winding the tape around the caps. Use tape wide enough that its edges extend past the caps and can be folded over into the inside of each cap. That way, threading the caps onto the bottles will also help keep the tape from peeling off.
Step 7: Mount the Trap, Attach the Capture Bottle
Drill a small drain hole through the lowest point of each small cup-shaped depression in the bottom of the Deer Park bottle. As shown in the Intro photo, I used two metal angle brackets and screws to fasten each of eight traps to the underside of the overhang of my mansard style roof, where I usually see the bees looking for places to bore. The trap can also be hung up by a wire or cord so long as it is placed where wind cannot cause the trap to swing and hit something.
I leave the traps in place year round and screw on the capture bottles just during bee season. It may be that bees caught in the capture bottles help attract other bees, so I am in no hurry to empty them. It may even be worthwhile to place some captured bees, dead or alive, into the bottles of empty traps, in order to enhance the attraction of the latter. This exercise is left to the reader. I do make sure that all the bees in a capture bottle are dead before I unscrew it from its trap in order to discard the bees.
Never use insecticide on any part of a trap, or near a trap, as doing so may repel the bees.