Do Carpenter Bees Eat Pressure-Treated Wood Decks?

Damage to Wood

Pressure-treated wood has been treated with various chemicals that are designed to make the wood last longer and be more resistant to insect damage. They can still present an attractive home to bees, however. Although carpenter bees will generally look for a piece of wood that is fairly soft, such as pine or cedar, they have been known to choose pressure-treated wood in which to dig their nests. The damage done comes in the form of long tunnels chewed through the wood. Carpenter bees don't actually eat the wood; the females simply use their strong jaws to hollow out holes and tunnels in which to lay their eggs. Tunnels are usually around 1/2-inch in diameter, and can extend between 2 and 12 inches.

Carpenter bees are solitary bees, which means that even if they do take up residence in a pressure-treated deck there will not be a large colony that develops throughout the summer months. Bees will generally begin to chew their nesting tunnels in the spring, and throughout the summer they will be seen stocking the tunnels with nectar and pollen for the young bees that hatch. Females can be more aggressive than males, which may cause a problem if several take up residence.

Because of the length of the L-shaped tunnels that the bees build, they prefer to nest in thicker pieces of wood that are at least 2 inches thick. Areas of the decking that are less than this will be highly undesirable as nesting sites.

A handful of tunnels from a few carpenter bees generally doesn't present an issue to the structural integrity of the deck, especially since there is only one bee per tunnel, and the network is not that extensive. There is the possibility of unattractive stains outside of the holes, as the bees tend to relieve themselves right before going into their tunnels.

Some of the problems associated with the bees come not from the activity of the bees themselves. Woodpeckers and other birds can damage the wood when they try to get at the bees and their larvae. The damage to the wood -- even pressure-treated wood -- can expose the wood to the elements as well as to mold and fungi that can get inside the tunnels.

Getting rid of carpenter bees can be time-consuming. One of the most effective ways is to fill the end of each tunnel with an insecticide developed for this type of bee. When done in the spring, this will kill many of the bees before they can lay their eggs. Applying the insecticide once in the spring and again in the late summer will help ensure that not only are the adult bees killed, but the newly hatched bees are as well. Since the bees will overwinter in their tunnels, applying insecticides in the fall months will help prevent problems the following spring. This is not a fool-proof plan, however, as new bees can begin building tunnels virtually anywhere they find exposed wood.