The Carpenter Bee Holes In Your Deck Are Not Empty Right Now

They are occupied. Ohio State University Extension says the adults that grow up in a carpenter bee gallery hibernate inside that same gallery over the winter and emerge the following spring. The holes under your deck rail are not leftovers from last May. They are where this winter is being spent, and they are where next May starts.

That changes what to do about them in October. Sealing a hole is the right idea in the wrong order, and the order is most of what follows. Our stinging insect control work covers the wasps and hornets that generate the emergency calls. Carpenter bees are the slow version of the problem, and fall is the stretch of the year when you can get in front of them.

What Is Actually Inside The Hole In October?

Adults, not an empty tunnel. Clemson Cooperative Extension describes adult female and male carpenter bees overwintering in abandoned nest tunnels in which they have stored small amounts of pollen, then emerging in spring, in April and May, to mate and look for nest sites. Ohio State University Extension puts it the same way from the other end: the new adults store pollen in the existing galleries, spend much of their time huddled together inside the gallery where they developed, and hibernate there until spring.

So the quiet is not progress. Nothing is going to leave that board between now and April on its own, which is the whole reason October is worth spending on this rather than waiting for the first bee to buzz the porch in the spring.

Why The Same Three Boards Get Hit Every Spring

Because a finished gallery is valuable and a new one is work. Ohio State University Extension notes that a female preferentially refurbishes an old nest rather than creating a new one, and the University of Maryland Extension describes tunnels being lengthened and reused year after year by successive generations. That is why the damage on a deck rail or a fascia board does not stay the same size.

A single season of tunneling in a rail is a cosmetic complaint. A beam that has been refurbished by successive generations for a decade is a different conversation, and nothing about the outside of the board tells you which one you are looking at.

The Woodpecker Is The Second Half Of The Damage

If a fascia board carries a row of round holes and a ragged trench torn open above them, two different animals made that. The University of Maryland Extension points out that woodpeckers cause further damage when they hunt for carpenter bee larvae, and a bird working a known gallery is not making half inch holes. It opens the board up.

That is worth knowing in October for a practical reason. The galleries are full of larvae and hibernating adults all winter, which is exactly what a woodpecker is looking for in the months when other food is scarce.

Is Fall Really The Time, Or Should This Wait For Spring?

Both windows are real, and the published guidance names them. The University of California Statewide IPM Program describes treating tunnels either in early spring, before nesting activity has begun, or in fall, after all adult bees have emerged and are settling in to hibernate through the winter. Penn State Extension builds the fall window into its schedule as well, with a treatment in early fall aimed at contacting the overwintering bees occupying the tunnels.

The fall window has one plain advantage. Everyone is home. In April the bees are flying, mating and prospecting for new sites, and a male hovering at head height in front of the garage is a nuisance that makes people swing first and think later.

Why Sealing Is The Last Step And Not The First

This is the part that goes wrong. The instinct is to reach for the caulk gun, because a hole is a hole. Penn State Extension says plainly not to plug the holes immediately, because the bees need to be able to pass freely through the entrance, where they pick up the treatment and carry it into the tunnel. Clemson gives the sequence a clock: treat, and after twenty four hours plug the tunnel entrances with wood putty, caulking compound or a wooden dowel coated with wood glue, which also stops other nesting bees from taking the gallery over. The University of California IPM guidance is the same shape, a day or two of waiting before anything gets sealed.

Caulk first and you have sealed a live gallery behind a plug and left the board on the menu. We do not publish application instructions, because the treatment half of that sequence is licensed applicator work in Ohio. The repair half is honest weekend work once the first half is done. If you want to know who is allowed to do which part, our post on checking an Ohio pest control license walks through it.

What Keeps Them Off The Board Next Year

Prevention here is about the surface and the material, and the sources are unusually consistent about which choices matter.

• Paint, not stain. Clemson calls a painted surface, oil based or polyurethane, the most effective deterrent to carpenter bee activity, and says wood stains provide little repelling action. That distinction matters on a cedar deck that has only ever been stained.
• Expect a deterrent, not a force field. Michigan State University Extension notes that painted or treated wood is less likely to sustain holes but can still be damaged. Paint moves the odds, it does not close the question.
• Change the material where it keeps happening. The University of California IPM program recommends building susceptible exterior parts of a structure out of hardwoods, which are not normally attacked for nest building.
• Fill the old galleries once they are handled. A refurbishable nest is the thing a returning female is looking for, so an open tunnel left over the winter is an invitation with an address on it.
• Walk the boards that actually get hit. Deck rails and the underside of rails, fascia and soffit edges, porch and pergola beams, outbuilding siding, swing sets, and the trim above a window where nobody ever looks up.

They Are Pollinators, Which Complicates It

Worth saying out loud, because it is true and it shapes the job. Ohio State University Extension is explicit that carpenter bees feed on nectar and pollen and do not consume wood at all. They are native bees doing native bee work, and the damage is a side effect of where they chose to raise young. The target is the galleries in a structure, not bees in a yard, and we take the same line on this that we take on pest control around pollinators generally.

State Termite has worked on Northeast Ohio houses since 1933, and a deck rail, a barn trim board and the fascia over the garage are the same question in North Canton and across Stark, Summit, Portage, Wayne and Tuscarawas counties. If there is a row of round holes on your place and you would rather not count ten of them next June, send it through our request form for a free estimate or call 330-494-6199.