Make Room for Pollinating Carpenter Bees
By Julie Pramuk
NAPA VALLEY, Calif. — For many years I’ve heard about carpenter bees, but this year my relationship with these amazing insects became close and personal. On one side of our 100-year-old house is a peach tree that stands about 7 feet tall in summer. The trunk curls around in a pleasing shape, but at one time a substantial branch was cut, leaving a surface of about 6 inches across.
While gardening under the tree one day, I spotted a large, fuzzy, golden-orange bee wiggle into a hole in this sawed-off branch. I realized I was looking at a carpenter bee. After that, I stayed clear of the area, not knowing how friendly the bee might be. It might not appreciate my scuffling around under the branch, which was less than 3 feet from the ground.
Several days later I saw a large pile of fresh sawdust on the other side of the cut-off branch. Hmm, I thought, there is definitely some serious carpentry happening here. A duplex, perhaps? I decided to find out more about my new neighbors.
The California carpenter bee (Xylocopa californica) is native to western North America. Carpenter bees are classified as long-tongued bees and are the largest native bees in the United States. They are a hefty 1 inch long, oval, with six legs and a pair of antennae.
The carpenter bee receives its name from its nesting habit. It digs into wood — often a dead tree or fallen log — to make a nest. The bees prefer softer, older wood, but in urban areas they will also make a home in new-construction wood. The bee makes its nest by creating long, double-ended passages in the limbs of trees, just as I saw it doing in my peach tree.
The female carpenter bee is solid black, while the male is commonly known as the “teddy bear bee” because of its fuzzy orange exterior and gold-green eyes. The male does not sting. The female, however does sting, and the result can be painful.
Male and female carpenter bees have different jobs. The sole responsibility of the female is to excavate a series of tunnels, using her powerful mandibles to make a home for her offspring. Tunnel entrances are about ½-inch in diameter, just big enough for the bee to enter. The tunnel interior may be an inch in diameter.
After she completes the tunneling, the female will create six to eight individual cells. She provisions each cell with a ball of bee bread, consisting of pollen and nectar. She will lay her eggs in the cells, then seal off the tunnel with sawdust. Eggs hatch and reach adulthood in about seven weeks. The adults remain in the nest for several weeks before digging their way out in the fall.
Females lay eggs only once a year. The new generation emerges in April and May and repeats this cycle. Carpenter bees might return to the same nest for many generations, expanding and renovating the nest year after year.
The objective of the male bee is to attract the female. The male lingers near a non-flowering plant, often near a food source, and releases sweet-smelling pheromones that lure the opposite sex. The male carpenter bee is always on the defense; after mating, its main job is to protect the nest. Although it does not have a stinger, its larger size and aggressive nature help it ward off unwanted visitors.
Carpenter bees might be a nuisance, but they are important pollinators. Approximately 15% of our state’s crops are pollinated by native bees.
Robbin Thorp, an emeritus professor of entomology at UC Davis before his death in 2019, was a renowned bee expert. He cited carpenter bees as important pollinators of crops such as passion fruit, blueberries, melons, tomatoes and eggplant.
“They may even pollinate flowers while ‘nectar robbing’ from them,” he wrote.
The carpenter bee’s practice of tunneling into wood is an initial step in the recycling process in natural communities.
We can encourage carpenter bees by creating nesting sites in our yards. All it takes is a few materials, such as wooden logs, boards or blocks. Planting nectar plants that provide food in each season will help them survive in an urban environment.
The bees’ nest doesn’t take up much real estate in my yard. I look forward to watching them remodel their home next year.
Napa Valley Features Note:
Creating a home for carpenter bees helps protect these important pollinators and provides them with an alternative nesting site. Follow these steps, adapted from the guidelines at Choose Timber, Hanbury House and The Pollinator Garden, to build a carpenter bee nest:
Materials Needed
Solid block of untreated wood (e.g., pine, cedar or Douglas fir)
Drill with 1/2- inch bit
Saw (miter saw, hand saw or circular saw)
Sandpaper (optional)
Nails or screws
Wood glue (optional)
Paint or wood sealer (optional)
Step-by-Step Instructions
1. Cut the Wood Block: Cut a block of wood to approximately 4x4 inches and 6-8 inches in length.
2. Drill the Holes: Using a 1/2-inch drill bit, drill holes 5-6 inches deep at an upward angle to prevent water entry. Space the holes a few inches apart.
3. Add a Roof: Cut a piece of wood larger than the block's top for an overhang. Attach it using nails, screws or wood glue.
4. Finishing Touches: Sand edges to remove rough spots (optional). Paint or seal the exterior to protect from elements (avoid inside of holes).
Placement
Mount at least 3 feet off the ground in a sunny location, ideally facing southeast.
Place near active carpenter bee areas.
Maintenance
Clean out the bee house at the end of the season to prevent mold, fungus and parasites.
Replace the wood block every year or two.
Additional Tips
Use weathered, untreated wood for the best results.
Provide alternative nesting sites such as brush piles or dead wood to attract bees away from your home.
By following these steps, you can create a welcoming home for carpenter bees, protecting these valuable pollinators and preserving your wooden structures.
Workshop: Join UC Master Gardeners of Napa County for “Growing Cool-Season Vegetables” on Saturday, Aug. 10, from 10 a.m. to noon at the University of California Cooperative Extension Office, 1710 Soscol Ave., Napa. From lettuce and carrots to more exotic greens and vegetables, many delicious choices await the fall and winter gardener. This hands-on workshop provides growing tips from planning and planting to harvest and into the kitchen. Register here.
Workshop: Join UC Master Gardeners of Napa County for “Growing Cool-Season Vegetables” on Sunday, Aug. 18, from 2 to 4 p.m., at Yountville Community Center, 6516 Washington St., Yountville. From lettuce and carrots to more exotic greens and vegetables, many delicious choices await the fall and winter gardener. This hands-on workshop provides growing tips from planning and planting to harvest and into the kitchen. Register through Yountville Parks and Recreation. After clicking the link, find the registration page at Adult Activity > UC Master Gardeners > Fall & Winter Gardening.
Fall Faire: Join the UC Master Gardeners of Napa County for an entertaining and educational event on Saturday, Sept. 28, from 1 to 4 p.m., outdoors at the University of California Cooperative Extension, 1710 Soscol Ave., Napa. Enjoy exhibits on composting, monarch butterflies, succulents, water conservation, bees and more. The program includes activities for kids, a scarecrow contest, giveaways and music. Admission is free.
Become a Master Gardener Volunteer: UC Master Gardeners of Napa County is now accepting applications for the Class of 2025. Click here to read the informational brochure, then register to attend a mandatory information session for applicants. Application deadline is 5 p.m. on Sept. 25.
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 a.m. until 1 p.m. at the University of California Cooperative Extension Office, 1710 Soscol Ave., Suite 4, Napa. Or send your questions to mastergardeners@countyofnapa.org. Include your name, address, phone number and a brief description. For best results attach a photo.
If today's story captured your interest, explore these related articles:
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Julie Pramuk is a UC Master Gardener of Napa County.
They drilled into my original greenhouse. I read that they will not go through latex paint and they have not drilled again. Good article Julie!!!!!!
A word to the wise: keep up on your own home maintenance. If you have wood siding, eaves, trim, keep them oiled or painted. Bees like old dry wood. They create tunnels and lay their eggs, which brings the woodpeckers. You then end up with two inch holes jackhammered into your house as the woodpeckers go after the larvae. Ain’t nature grand? 😏