If you’ve noticed perfectly round, dime-sized holes appearing in your deck railing, pergola, or the eaves of your shed, and you’ve seen a fat, shiny bee hovering nearby like it’s guarding the place — congratulations, you’ve got carpenter bees. They look almost exactly like bumblebees, except their abdomens are smooth and black instead of fuzzy and yellow. That’s the tell. And unlike bumblebees, they’re not remotely interested in pollinating your garden. They’re interested in your wood, and they will happily bore through it to raise a family inside.
Why They Love Your Deck Specifically
Carpenter bees go for bare, unpainted, unfinished wood, especially softer woods like cedar, redwood, and pine. That’s most decks, most of the time. The females drill a hole about half an inch wide, then turn a sharp corner and tunnel with the grain for several inches to build a series of little nursery chambers. One female might not do much damage. A few years of the same tunnels getting reused and extended by new generations, though, and you’re looking at real structural weakening in railings and posts.
The males are the ones that dive-bomb you near the nest entrance, which is unsettling but mostly theater — they don’t have stingers. The females do have stingers and can use them, but they’re not aggressive unless you’re actively grabbing at their tunnel.
What Actually Works
A lot of the advice floating around is half-measures at best. Spraying the bee itself when you see it flying around does nothing for the ones already inside the wood, and there are always more inside than you’d guess. Here’s what actually moves the needle:
- Treat the holes directly, at dusk. Carpenter bees are least active in the evening. Use an insecticidal dust (not spray) labeled for wood-boring insects, and puff it directly into each hole with the little applicator that usually comes with it. Dust works better than liquid spray here because the bees track it around inside the tunnel and it keeps killing for days.
- Wait a couple of days, then plug the holes. Don’t seal them immediately — you want any bees still inside to make contact with the dust first. After 48 hours or so, fill each hole with wood filler, a wine cork, or a dowel and wood glue, then sand it smooth.
- Paint or stain the wood. This is the step everyone skips and it’s the one that actually prevents round two. Carpenter bees strongly prefer bare wood. A coat of paint (better than stain, which they’ll still occasionally tolerate) makes the surface far less appealing for new nesting next spring.
- Hang up a decoy nest or two if you’re feeling generous. Some people install a small block of untreated scrap wood nearby as a sacrificial nesting spot, away from the structural parts of the deck. It doesn’t always work, but it costs nothing to try and occasionally redirects traffic.
Timing Matters More Than People Think
Right now, in early July, you’re dealing with an active generation that’s been tunneling since spring and is currently provisioning chambers with pollen for larvae. Treating now interrupts that cycle before a new batch of bees emerges in late summer and starts the whole thing over. Wait until fall and you’ve just let another generation mature and disperse, which means more holes to find next year.
When to Call Someone
If the infestation is up near a roofline, inside fascia boards you can’t easily reach, or you’re finding a dozen-plus active holes, it’s worth bringing in a pest control pro. Chronic, untreated infestations do add up over years — enough tunneling can genuinely compromise a railing or post, and finding that out because someone leaned on it wrong is a worse afternoon than paying for a treatment now.
The unsatisfying truth is there’s no one-and-done trick here. It’s dust, patience, filler, and paint — in that order. Skip the paint step and you’ll be back here again next July, holes and all.
