Godwin Column: Dealing with carpenter bees

Carpenter bees once again are excavating tunnels for nesting sites. Coarse sawdust is on my deck and at the base of a storage building.

Carpenter bees target wooden decks, overhangs, exposed wood and wooden furniture. They prefer untreated and unpainted wood, but treated and painted surfaces also may be attacked.

Shingles and siding made from cedar, cypress and redwood also are attacked in spite of their reputation as pest-resistant. These bees do not eat wood but remove wood with their strong jaws, leaving a round, half-inch diameter entrance hole to a new nesting site.

Carpenter bees are large, and black and yellow in color. They resemble a bumble bee, so look closely for the black shiny tail section to distinguish them.

This bee over-winters inside the old nest tunnels as an adult, coming out in April and May. Males have a whitish spot on their face, which females do not. The males defend their territory aggressively but do not have stinger. Females usually sting only if harassed or provoked.

After emerging in the spring, they feed on plant nectar and begin constructing new tunnels. The build galleries along the grain of the wood, maybe as long as 12 inches.

The female bee gather pollen and forms it into a large ball to feed the young. She deposits the pollen ball with an egg, sealing off small sections of the tunnel. The adult bees die before the new brood emerges. The young bees feed on pollen and clean out the established tunnels where they will over-winter when the weather cools.

Carpenter bees do not usually cause major structural damage, but a large number of active bees for several years in a row should be avoided. Thin wood is especially vulnerable to severe damage. Surfaces exposed to the elements may have additional damage by fungi causing decay in the wood.

Avoiding damage from carpenter bees is very difficult. Bees are only active for a short time while insecticidal sprays are efficient for a short time. Carpenter bees do not eat wood, so exposure to a pesticide is nominal. It is quite difficult to apply a pesticide to all possible tunneling sites. Using a racket to swat bees out of the air is just as effective (and safer) than trying to apply a pesticide to hovering bees.

If pest control is warranted, treat the holes with an insecticide and plug the holes with a ball of aluminum foil. Caulk the plugged holes after allowing the pesticide 24 to 36 hours to work. Without the pesticide application, live adults may emerge later or make another exit by chewing another hole.

 Peg Godwin is horticulture agent, Lenoir County Cooperative Extension Center. Reach her at Peg_Godwin@ncsu.edu or (252) 527-2191.