How to Deal with Carpenter Bees

Chances are you’ve been buzzed by a large, intimidating-looking bee when working on the outside of your home. You may also have the telltale holes in your woodwork where these bees build their nests.

About Carpenter Bees

Carpenter bees are large black and yellow bees that resemble bumblebees. But while bumblebees are fuzzy all over; carpenter bees have a large, shiny, solid black abdomen.

While they may look scary, male carpenter bees – the ones most likely to dive-bomb your head with a whitish spot on their face – don’t even have stingers, and females generally won’t sting unless you aggravate them.

Carpenter bees get their names by the perfectly round, half-inch or so diameter holes that they drill in wood for their nests. In the spring, the bees emerge from their winter nests, mate, and set about building this year’s nest.

The female bee uses sharp teeth to excavate a perfectly round tunnel in soft wood, or she may choose instead to remodel an existing tunnel. She then lays her eggs in the tunnel, where they develop as her life cycle comes to an end.

In late summer, the new bees emerge to feed on plant nectar, then crawl back into their hole for the winter.

Carpenter Bee Damage

Carpenter bees prefer to excavate their nests in soft, unpainted wood – such as the back side of fascia boards, siding, window trim, and porch ceilings. They also bore into decks, outdoor furniture, fence posts, and swing sets. Softer woods – like pine, cedar, redwood, and cypress – are more attractive for nests while treated lumber and hardwoods are less inviting.

The holes typically go inward for about an inch, then the tunnel turns and follows the grain of the wood for about six more inches. The tunnel might branch into smaller ones that are shared by multiple bees.

In addition to tunnels, you might also find:

• Fresh sawdust outside the hole.
• Scraping sounds from inside the wood.
• Fan-shaped stains outside the openings.

If your infestation is limited to a tunnel or two, there’s nothing to worry about. Even though they technically do bore into wood, carpenter bees don’t systematically destroy a structure like termites or carpenter ants.

However, if the infestation is extensive or has been going on for years, the sheer number of tunnels can cause problems, including:

• Structural Damage: It would take a lot of tunnels to compromise a structure, but over time they can weaken wood.
• Water Damage: If moisture enters the tunnels, it can speed the rotting of the wood. This is especially problematic if the tunnels are in your home’s siding, since it protects the structure.
• Stains: Feces of carpenter bees can stain wood.
• Woodpeckers: Insect eating birds can be drawn to the enticing sounds of bee nesting and larvae, which can invite much more severe damage.

How to Prevent Carpenter Bee Damage

Here are some tips for making your home less attractive to carpenter bees:

• Paint or Varnish: You can discourage carpenter bees by painting all surfaces (including the backs and undersides of boards) with a sealing primer and at least two coats of paint. Stains and varnishes are less effective, but any coating is better than bare wood.
• Treated or Hard Lumber: Treated lumber and hardwoods are less susceptible to damage from carpenter bees.
• Non-Wood Covering: If the problem is unrelenting, you may need to look into non-wood siding and trim options, such as aluminum, vinyl, fiber cement, or masonry.
• Fill Cracks: Before painting or sealing, fill all cracks, nail holes, divots, and splintered wood with caulking or putty; since these are attractive starting places for bees.

How to Deal with Carpenter Bees

If the bees are already at work on your home:

• Fill Abandoned Holes: When carpenter bees emerge in spring and again in fall, fill holes with a bit of steel wool, a wad of aluminum foil, a dowel and wood glue, or even caulk. After filling the holes completely, paint over them.
• Treat Active Holes: If the holes are still active, you may want to treat the holes with a targeted dose of insecticide first. Products such as pyrethrum, boric acid, carbaryl (Sevin), or any spray labeled for flying insects will do the trick. The best time to treat the holes is at night when bees are resting, or in early spring while they’re still hibernating. Apply the spray or powder directly in the hole, staying on alert for an angry female bee that might emerge. By the next day, you should be able to fill and paint over the tunnel.
• Avoid Wood Treatments: Since carpenter bees don’t actually eat wood, treating it doesn’t do much good.
• Stay Alert: There’s no way to completely prevent or eliminate carpenter bees. But by taking these steps and staying alert to new activity, you can keep damage to a minimum.

Further Information

• Carpenter Bees (North Carolina State University)
• Carpenter Bees (University of California Integrated Pest Management)