Perfectly round holes under the deck rail, a little pile of sawdust on the boards below and a big black bee hovering at eye level all point to carpenter bees. They don't eat wood, but they tunnel into it to raise their young, and they come back to the same boards year after year. The best protection depends on what your deck is made of and how it's finished. That's where most advice goes wrong. Here's what university entomologists in the Carolinas, Kentucky and Georgia say actually protects deck wood, and which popular fixes have never been tested.
Paint is the best long-term protection. Clemson Extension calls an oil-based or polyurethane painted surface "the most effective deterrent," and says stains offer little protection. Bare, weathered cedar, cypress, redwood and pine are the favorite targets. Pressure-treated wood is less preferred but not immune.
For active holes: treat each hole with a labeled insecticide dust or spray in the evening, leave it open a few days, then plug it with a glued wooden dowel or putty. Traps can catch bees, including egg-laying females, but nobody has published a peer-reviewed test showing they protect wood.
Which Deck Wood Carpenter Bees Attack
University of Kentucky entomologist Michael Potter says carpenter bees "prefer unpainted, weathered wood, especially softer varieties such as redwood, cedar, cypress and pine." UGA Extension adds that they go for old, unpainted wood in particular. Typical deck targets are rail undersides, joist ends, fascia boards, pergola rafters and outdoor furniture.
| Wood or finish | Risk | What extension sources say |
|---|---|---|
| Bare, weathered cedar, cypress, redwood, pine | Highest | Preferred by carpenter bees (UKY, UGA) |
| Stained or sealed wood | Still high | Clemson and NC State: stains give little repellence. UKY: "less reliable than painting" |
| Pressure-treated pine | Lower | UKY: "much less susceptible." NC State: painted and treated wood are less preferred "but by no means immune" |
| Painted (oil-based or polyurethane) | Lowest | Clemson: "the most effective deterrent." NC State: not immune. UKY: "usually will not tunnel into painted wood" |
Homeowner experience fits the table. On Reddit, one owner found solid stain "definitely works better than the semi-solid stain, but it's not 100%." A deck builder warned that "some carpenter bees chewed right into some PT painted" lumber. Paint has a practical downside on walking surfaces: one homeowner "painted my deck and have regretted it ever since," because deck paint wears faster than stain. The practical compromise is to paint the parts bees attack, like rail undersides, fascia, joist ends and pergola beams, even if the deck boards themselves are stained.
Signs Carpenter Bees Are in Your Deck
- A round hole about 1/2 inch across. UKY compares it to the diameter of your little finger. The edges are clean, not ragged.
- Coarse sawdust on the boards or ground below.
- Yellowish-brown streaks below the hole. NC State identifies this as the bees' waste, not pollen, and notes it's hard to clean off glass and car paint.
- Males hovering near the deck in spring. They look aggressive, but UKY confirms males can't sting.
- Woodpecker gouges. Woodpeckers rip into boards to reach the larvae, which UGA notes adds structural damage on top of the tunnels.
How the Damage Builds Over Time
A female bores in a short distance, turns at a right angle and tunnels along the grain. Clemson puts a typical tunnel at 4 to 6 inches, with about five or six egg cells inside according to UKY. One tunnel is minor. The problem is reuse. Adults spend the winter in old tunnels, emerge and mate in spring, and females enlarge old galleries or dig new ones next to them. Clemson says repeated use can extend tunnels up to 10 feet, and UKY warns that "significant damage can occur when the same pieces of wood are infested year after year." The open holes also let in water, which UKY notes leads to rot and decay.
In South Carolina, Clemson says adults emerge in April and May. Activity can start earlier farther south, where UGA reports adults emerging in February in Georgia. New adults appear in late summer, feed on flowers, and return to the wood in fall to overwinter.
How to Stop Carpenter Bees From Drilling Your Deck
1. Paint the parts they attack
This is the most durable fix. Use an oil-based or polyurethane paint on rail undersides, fascia, joist ends, beam ends and any other bare or weathered wood, paying special attention to end grain. Keep the finish up. Once it wears through, the wood is back on the menu.
2. Treat active holes, then plug them
- Treat in the late evening, when bees are inside. Clemson recommends late evening or night. Females defending a nest can sting, so wear protective clothing.
- Puff or spray a labeled product into the hole. UKY lists dusts, liquids and aerosols containing bifenthrin, cyfluthrin, deltamethrin or lambda-cyhalothrin. Follow the label.
- Leave the hole open for a few days (Clemson says at least 24 hours) so returning bees pick up the insecticide and spread it through the tunnel.
- Then plug it with a wooden dowel coated in carpenter's glue, wood putty or caulk. UKY says this discourages reuse and keeps moisture out.
Plugging an untreated hole in spring can trap a live bee, which will just chew a new exit. Treat first, then seal.
3. Surface sprays are a short-term deterrent
Spraying vulnerable wood with one of the same pyrethroids makes some bees avoid drilling there, but UKY says it lasts only about 3 to 4 weeks, and UGA puts it under 4 weeks. It's a bridge until you can paint, not a fix. Keep sprays off flowering plants, since carpenter bees and other bees are pollinators.
This is the method in the most-watched carpenter bee deck video on YouTube (about 1.3 million views), where homeowner Adam J sprays permethrin, another pyrethroid, on the underside of his deck. In his three-week update the bees had stopped mobbing the deck, but he said he didn't know how long it would last and expected to respray about once a month. That fits the 3 to 4 weeks the extension services give. One commenter sprays twice each spring, about three weeks apart, and calls permethrin safe for all vertebrates. It isn't. The National Pesticide Information Center says it's highly toxic to fish and to bees, and that cats are more sensitive to it than dogs or people.
4. Traps: worth trying, but unproven
Carpenter bee traps are wooden boxes with 1/2-inch holes that funnel bees into a bottle. UKY suggests hanging them at the corners of the house, porch or deck in early spring. The evidence is thin, though. UGA's IPM program says there have been no objective, peer-reviewed evaluations of traps or repellents for managing infestations. A small Cornell trial in New York caught 54 carpenter bees in 12 traps, including 33 egg-laying females, and residents at the worst site noticed a big drop in activity. The same traps also caught 148 other arthropods, including paper wasps and yellowjacket queens. Use traps alongside paint and hole treatment, not instead of them.
5. Rebuild with less attractive materials
When you replace rails, trim or pergola parts, use painted lumber, pressure-treated lumber that you paint, or non-wood materials like composite or vinyl trim. One homesteader on Reddit answered the "best coating" question with two words: "Sheet metal." That's an option for fascia and trim.
Fixes That Don't Hold Up
- "Stain will keep them out." Extension sources agree stains give little protection. Solid stain is better than semi-transparent, but not reliable.
- "Essential oils repel them." Citrus, clove and citronella oils are popular online, but UGA says repellents haven't been objectively tested.
- "Steel wool and caulk without treatment." Sealing an active tunnel without treating it first can trap bees that simply chew out.
- "Pressure-treated wood is immune." It's less preferred, not bee-proof, especially once it weathers.
When to Call a Professional
- Holes in high eaves, pergola rafters or second-story trim you can't safely reach
- Woodpecker damage or soft, hollow-sounding boards
- Activity across several parts of the house, not just one rail
- Round holes you aren't sure are carpenter bees, since a termite inspection is a different job
Our stinging insect control service treats carpenter bees across South Carolina, North Carolina and Virginia. For removal methods beyond the deck, read how to get rid of carpenter bees, and see whether wasps are dangerous if you're sharing the deck with paper wasps too.
Key Takeaways
- Bare, weathered softwood is the target. Cedar, cypress, redwood and pine top the list.
- Paint beats stain. Oil-based or polyurethane paint is the best deterrent. Stains offer little protection.
- Pressure-treated wood is less attractive, not immune.
- Treat holes in the evening, wait a few days, then plug with a glued dowel or putty.
- Surface sprays last only 3 to 4 weeks. Traps and repellents haven't been proven to protect wood.
- Damage builds as bees reuse the same boards, so act in the first season.
Sources: M. F. Potter, "Carpenter Bees", University of Kentucky Entomology ENTFACT-611 (revised 2026); W. M. Hood, revised by K. Roach, "Carpenter Bees", Clemson Cooperative Extension HGIC (2020); NC State Extension, "Carpenter Bees", Entomology Insect Note (2018, archived); UGA Cooperative Extension, "Carpenter Bees: A Serious Pest of Wooden Structures in the Landscape", Circular 1342; UGA IPM, "Eastern carpenter bee" (2026); Cornell University, "Carpenter Bee Trap Evaluation", eCommons; National Pesticide Information Center, Permethrin General Fact Sheet; Adam J, "The BEST way to get rid of carpenter bees. They were destroying my deck!", YouTube; homeowner accounts from Reddit (via Google search excerpts) and YouTube comments.
Frequently Asked Questions
Paint the parts they attack, such as rail undersides, fascia, joist ends and pergola beams, with an oil-based or polyurethane paint. Treat active holes with a labeled insecticide in the evening, leave them open a few days, then plug them with a glued wooden dowel or putty.
Not reliably. Clemson and NC State Extension say stains offer little repelling action, and the University of Kentucky calls them less reliable than paint. Solid stain does better than semi-transparent, but paint is the most effective deterrent.
Less often, but they can. The University of Kentucky says painted or pressure-treated wood is much less susceptible, and NC State says painted and treated wood are less preferred but by no means immune, especially once it weathers.
Bare, weathered softwoods, especially redwood, cedar, cypress and pine, according to University of Kentucky and UGA entomologists. Rail undersides, fascia boards, eaves and joist ends are common targets.
They catch bees, sometimes including egg-laying females, but UGA's IPM program says there are no objective peer-reviewed evaluations showing traps protect wood. A Cornell trial caught 54 carpenter bees in 12 traps along with 148 non-target insects.
Yes, but treat them first. Apply a labeled dust or spray into the hole in the evening, leave it open for at least a day or a few days so bees contact the insecticide, then plug it with a wooden dowel and carpenter's glue, putty or caulk to keep out moisture and future bees.
Clemson Extension says adults emerge in April and May. They overwinter as adults in old tunnels, mate in spring, and females drill new tunnels. New adults appear in late summer and return to the wood in fall.
One tunnel is minor, typically 4 to 6 inches, but bees reuse and extend the same galleries every year. Clemson says repeated use can create tunnels up to 10 feet long, and the holes let in moisture that leads to rot. Woodpeckers hunting larvae add more damage.
No. Males, identified by the pale patch on their face, hover aggressively near nests but cannot sting. Females can sting but rarely do unless handled.
It's the bees' waste. NC State Extension describes yellowish-brown staining from voided fecal matter below the hole, and notes it can be hard to clean off glass and car paint.
Photo credits: Rhododendrites, CC BY-SA 4.0, via Wikimedia Commons; USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA, Public domain.