The large, bluish-black carpenter bee is out in full force every spring, seeking unprotected wood around your home to nest in. Carpenter bees bore 1/2-inch diameter holes and tunnels up to 6 inches long in weathered or unpainted wood. They typically prefer horizontal pieces, such as porch railings or siding. The bees don't eat the wood as they excavate, but structural damage can result from repeated nesting, woodpeckers trying to reach the growing grubs, or if water is allowed to penetrate the surface. It's possible to treat a carpenter bee infestation and prevent future nesting without an exterminator.
Get rid of an infestation by applying insecticides like boric acid an aerosol form of pyrethrin into the carpenter bee tunnels. A wasp-killing spray will kill adult carpenter bees, but even if you kill them, the grubs in the nest will survive and start the cycle again. Inject an insecticide dust into the holes with a long, tube-style spout applicator. The bees will carry the dust into the nest, killing the grubs.
Leave the insecticide-treated holes open for at least 24 hours and up to a few days before sealing them up to make sure the bees are dead; otherwise, they will bore new holes to get out. Seal the holes with exterior caulk, wood putty or a wood dowel glued in place. Apply a coat of paint or vanish to reduce the chance new bees will nest in the same area.
Reduce carpenter bee populations by hanging carpenter bee traps around your yard before the bees emerge in the spring from the tunnels where they spent the winter. Fill any existing carpenter bee holes so the bees will enter the traps instead. Some traps hold poisons to kill the bees or adhesives to trap them. Others simply are built so the carpenter bees cannot get out and will eventually die. Empty the traps regularly and leave them up until fall.
Prevent carpenter bee infestations by using treated lumber for outdoor projects and applying several good coats of high-quality polyurethane or oil-based paint to all exposed wood surfaces. Consider covering exposed fascia boards wtih aluminum flashing or vinyl siding. Regulary apply water-soluable spray products, designed for homeowner use to kill and repel carpenter bees.