Carpenter bees demanding actions

We are experiencing a swarming season for carpenter bees, which means they are foraging, mating and producing.

The ones buzzing around with a white or light yellow spot on front of their heads are males, and are aggressive but harmless.

The following are the most frequently asked questions I get about carpenter bees.

Where are they most likely to nest?

They are most likely to rest on eaves, window trim, facial boards, siding, decks, outdoor furniture and sometimes fences.

What kind of damage they do while swarming?

After mating, the females burrow into wood to lay eggs with a series of small cells. Each cell is provisioned with a ball of pollen; this is why you see them come in and out of the holes frequently before the holes are sealed. Each ball of pollen serves one larva. It is easy to identify the holes made by carpenter bees: they are round and about the diameter of a dime. This is the kind of damage they cause to wood, and it can be considerable if the wood has been utilized for nesting year after year.

What kind of wood do they not like to burrow into?

No wood is immune, but painted or pressure treated wood is less susceptible to attack.

How to control?

Liquid sprays of carbaryl (Sevin), chlorpyrifos (Dursban) or a synthetic pyrethroid, and all pesticide labeled for control dry-wood termites can be applied as a preventive to wood surfaces which are attracting bees.

Residual effectiveness of these insecticides is often only 1-2 weeks, however, and the treatment may need to be repeated because carpenter bees are active during the entire late-spring and early summer. Tunnels that have already been excavated are best treated by puffing an insecticidal dust into the nest opening. Aerosol sprays labeled for wasp or bee control also are effective. Leave the holes open for a few days after treatment to allow the bees to come in contact with the insecticide and distribute it throughout the nest galleries. Then plug the entrance hole with a piece of wooden dowel coated with carpenter’s glue, or wood putty, or simply caulk seal the holes. This will protect against future utilization of the old nesting tunnels and reduce the chances of wood decay.