Carpenter Bee Holes in Your Deck: What to Do

How do you know the holes came from carpenter bees?

Several signs show up together. If you see two or three of them, you almost certainly have carpenter bees.

• A clean, round entrance hole roughly the width of your finger, drilled straight into the face of a board.
• Coarse, pale sawdust piled on the deck surface, the ground or a lower rail.
• A brown or yellow stain streaking down the wood below the hole.
• Large bees hovering near the eaves in spring. The males dart at you but cannot sting. Females can sting, though they rarely do unless handled.
• A faint scratching sound from inside a post or rail on a quiet afternoon.

Is it carpenter bees, beetles or ants?

Other insects chew wood too, and the hole tells them apart. Getting it right matters because the fix for one will not touch the others.

Bumble bees do not drill wood at all. If the hole is the size of a finger and the wood is bare, assume carpenter bees until someone shows you otherwise.

Why do carpenter bees pick your deck?

A female chews in across the grain, turns, and digs along it to build a tunnel with small chambers. In each chamber she leaves pollen and one egg. The sawdust you sweep up is the wood she removed.

She prefers softwood that is bare, weathered or thinly stained, which describes many decks, pergolas and older porch rails around Columbus. Worthington's older neighborhoods are a good example, since the median home there dates to about 1963 (U.S. Census ACS 2019 to 2023) and decades-old trim has had decades to dry out. Bees reuse old tunnels and extend them, so a small problem this year grows by the third summer.

How much damage does a tunnel really do?

One year of one tunnel is mostly cosmetic. The entrance hole and the first few inches of gallery take little strength out of a board. The trouble builds when later generations extend the same tunnel and new females drill beside it. A rail or a post with several tunnels loses strength, and moisture follows the holes into the wood.

That is why the third summer matters more than the first. A joist, a post or a ledger board with many tunnels is worth having a carpenter look at.

What should you do about carpenter bee holes this month?

Match the work to the season. Adults come out in April and May to mate and nest, and a second wave of young adults appears in late summer.

1. Count the holesCheck rails, posts, the underside of the deck and the fascia. Note which holes have fresh sawdust, because those are active.
2. Treat each active tunnelA product labeled for the job goes into the hole, applied per label directions. Dust formulations travel along the tunnel better than a spray on the surface.
3. Leave the holes open for a whileBees need to travel through treated tunnels, and a hole plugged on day one can trap a live bee that tunnels out sideways.
4. Seal once activity clearly stopsUse a wood plug, dowel or filler pressed into each hole, then caulk and refinish the surface.
5. Check again in late summerNew adults emerge from tunnels you missed. Anything fresh gets the same treat, wait and seal sequence.

Which wood do carpenter bees pick, and which do they skip?

The bees look for bare, soft, dry wood. Wood that is painted, varnished or heavily stained gives them less to bite into. Use this as a guide for what to refinish first.

Bees often start at the underside of a rail or the end grain of a board, where the paint is thinnest. Look there first.

When should you seal carpenter bee holes?

Seal after the treatment has had time to work and you see no new sawdust or bee traffic at the hole. For most decks that means later in the season, not the same week as the application. Sealing early is a common mistake.

Once the hole is plugged, finish the wood. Paint or a good exterior stain leaves the bees less to like about the surface, and a coat of finish also protects the plug. Our carpenter bee control page explains the whole sequence in more detail.

How do you keep carpenter bees from coming back?

• Keep wood painted or stained. Bare boards are the main draw.
• Walk the property each April and look at the undersides of rails and the ends of boards.
• Replace boards that are riddled with tunnels instead of patching them.
• Fill old, abandoned holes after treatment so no one reuses them.
• Do not wait on a bad year. A few tunnels this spring is a smaller job than a dozen next spring.

If you are not sure whether another stinging insect is nesting nearby, our stinging insect removal overview shows what each one looks like.

Do traps and surface sprays help?

Wooden box traps catch some bees and can lower the number returning in spring. They do not treat the tunnels already drilled into your deck, so they work as a supplement, not a fix. A spray on the surface of the wood rarely reaches the tunnel, which is why a product labeled for the job goes into the hole itself.