It's bad news for your porch and deck.
Carpenter Bees
Credit: Tahreer Photography/Getty Images

Ever hear of the Law of Unintended Consequences? It expresses the thought that sometimes an action taken to make something better ends up making something worse. And that's certainly the case when it comes to the EPA, pressure-treated lumber, and a pest called the carpenter bee.

You probably have carpenter bees buzzing around your house right now. They're almost dead ringers for nice, beneficial bumblebees, but there's an easy way to distinguish them. Bumblebees have yellow, hairy abdomens. The abdomens of carpenter are hairless and glossy black.

Carpenter bees damage wood by boring perfectly round, half-inch wide holes into it to lay eggs and build a tunnel-like nest. They don't eat the wood like termites do—they just excavate it. I think they must have the strongest mandibles in the world, because they can quickly bore through wood too hard to drive a nail into like a hot knife moves through butter. Each year the bees locate the old holes, clean them out, and enlarge the chamber to raise more young. Over time, this can seriously weaken the wood.

These insects used to be the bane of mainly weathered, untreated wood like old fence posts or unpainted siding. Carpenter bees typically avoided stained or painted wood (and still do, though they may still attack it). To avoid bee damage to newly built wooden decks and porches, people relied on pressure-treated lumber containing CCA – chromated copper arsenate. The chemicals in CCA prevented rot and insect damage. I've dug up pieces of old pressure-treated lumber buried in the ground for 20 years and not found a single insect hole.

In 2003, however, the EPA banned the use of arsenic in pressure-treated wood used for home construction, claiming that it leached into the ground and posed a hazard. Pressure-treated lumber now contains the preservative ACQ, which stands for "alkaline copper quat." It was claimed that the higher concentration of copper in ACQ would compensate for the insecticidal arsenic no longer there.

It did not. It does not. It will not.

Yesterday, I ventured across the street to inspect a 25-year old deck built with CCA pressure-treated lumber. It has not received the slightest maintenance in its life, yet there is not a single mark on it except for normal weathering. No termite damage, no carpenter bees. Then I came home to discover four new carpenter bee holes in my ACQ pressure-treated deck that isn't six months old. This is why I instructed the builders that no posts supporting the deck were to come into ground contact, even if they are labeled for it. If carpenter bees bore right through the wood, imagine what termites might do.

Oh, and that's not the only problem with the new pressure-treated wood. Remember the higher concentration of copper in ACQ? Well, you better not use aluminum nails or flashing with this wood, because the copper and aluminum generate a tiny electrical current that quickly corrodes the aluminum. Boom! Deck falls down. Use only stainless steel or galvanized steel nails and flashing.

How To: Carpenter Bee Control

To kill and discourage carpenter bees, it's important to know where they like to attack. They like lumber that's at least two inches thick, like a rail or joist, and they bore in the narrow underside where you're least likely to see them. Little piles of sawdust on or under your deck mean bees are working. What I do is fill up a tank sprayer with Bayer Advanced Carpenter Ant & Termite Killer Plus (yes, I know, it says, "carpenter ant," but it also works on carpenter bees) according to label directions. I stick the spray nozzle into the hole and soak it. I then spray the narrow undersides of all rails and joists to prevent new holes. After 24 hours, I use wood filler to fill holes I sprayed yesterday. Unfilled holes act like magnets for bees.

What about carpenter bee traps for people who don't like insecticides? (You can buy these online and at home centers.) I have some. While they do catch bees, they don't catch enough. It's like using Japanese beetle traps to guard your roses. You can catch enough beetles to fill the traps, but your roses are still devoured.

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I want to thank the EPA for forcing the replacement of a good product with an inferior one. The bees thank you too.