Carpenter Bees: They Don't Eat Your Wood, But They'll Wreck It Anyway

I spent two summers ignoring the fat bees hovering around my deck railing before I flipped a board over and found Swiss cheese. Dozens of tunnels, some over a foot deep, boring through what used to be solid cedar. That's when I actually bothered learning what carpenter bees do. Turns out they're not eating your wood. They're raising families in it.

What Carpenter Bees Are Actually Doing

Every spring, a female carpenter bee picks a piece of untreated, unpainted softwood and drills a perfectly round hole. About half an inch in diameter. She goes straight in for an inch, then makes a 90-degree turn and tunnels along the grain for 6 to 10 inches. Inside that tunnel, she lays eggs in individual cells separated by walls of chewed wood pulp.

She's not eating. She's building a nursery.

The problem is that carpenter bees reuse and extend the same tunnels year after year. A tunnel that started at 6 inches becomes 10 inches the next spring. Her daughters come back to the same board and drill new branches off the original tunnel. Three or four generations in the same piece of wood and you've got a structural problem. I've seen deck joists and fascia boards that looked fine from the outside but crumbled when you grabbed them. Woodpeckers make it worse. They hear the larvae inside and hammer holes into the wood to get at them, turning neat half-inch entry holes into ragged craters.

Males Can't Sting, Females Won't Bother

The big ones dive-bombing your face on the porch? Those are males. They're aggressive and territorial and completely harmless. Males don't have stingers. They're all bluff.

Females have stingers but almost never use them. You'd basically have to grab one and squeeze it. If you're getting stung by something near carpenter bee holes, it's probably a wasp. Check our stinging insects guide if you need help telling them apart.

How to Tell If You Have Them

Look for perfectly round holes, about the diameter of your pinky finger, in bare or weathered wood. Deck railings, fascia boards, porch ceilings, fence posts, wooden swing sets, and the undersides of outdoor furniture are all fair game. You'll see sawdust piles on the ground below the holes. The sawdust is coarse, not fine like powder post beetle frass.

Painted or stained wood is almost never targeted. They want bare softwood. Cedar, pine, redwood, cypress.

Treatment: What Actually Works

Timing matters. You want to treat in spring when the adults are active and in fall when you seal up the holes. Here's what I did and it's worked three years running.

Step 1: Dust the existing holes. Wait until evening when the bee is inside, then puff Drione Dust ($25 for a can that'll last you years) into each hole. A hand duster like the Bellow Bulb Duster ($12) works. The dust coats the tunnel walls and kills larvae, adults, and anything that passes through. Don't plug the holes yet. You want returning bees to contact the dust.

Step 2: Plug holes in October. Once activity stops in fall, stuff steel wool into each hole and seal over it with wood filler or a wooden dowel and wood glue. Steel wool matters because bees can chew through caulk and filler alone.

Step 3: Protect the wood. Paint or stain every piece of exposed wood. Two coats of exterior paint is the single most effective long-term deterrent. If you don't want to paint, spray NBS30 repellent ($18 per quart) on bare wood surfaces in early spring. It's a borate-based repellent that makes the wood taste terrible to them. Reapply after heavy rain.

When to Call a Pro

If you've got a dozen holes scattered across different parts of the house, or damage in hard-to-reach spots like soffits and roof trim, a pest control company can treat everything in one visit. Expect to pay $150 to $300. They'll dust the holes and apply a residual spray to exposed wood surfaces.

For a single deck or porch with a few holes, save your money and handle it yourself. The Drione dust and NBS30 spray together cost under $50 and cover a lot of ground.

The Bottom Line

Carpenter bees aren't dangerous and they're actually good pollinators. But ignoring them isn't an option if you care about your wood. The damage compounds every single year. Paint your wood, dust the holes, seal them in fall. It's one of those problems where 30 minutes of work in the right season saves you thousands in repairs later.