Carpenter bees

We're under attack.

Carpenter bees are all around the Zen house. There are holes in the underside of the rails of my side porch - right where my outdoor container herb garden is situated. I also see these bees buzzing around the eaves of the house.

We're going to do something about them, pronto. I've have already been using insecticide spray. Now I'm going to plug up the holes with foam.

Carpenter bees look a lot like bumblebees. The difference: bumblebees have an additional yellow stripe on their lower section, which is also noticably hairy. Carpenter bees lack the additional yellow stripe, and their lower section is smooth and shiny - no hair.

And carpenter bees tunnel into wood. Bare, unpainted or weathered softwoods are preferred, especially redwood, cedar, cypress and pine. Painted or pressure-treated wood is much less susceptible to attack. Common nesting sites include eaves, window trim, facia boards, siding, wooden shakes, decks and outdoor furniture. Bumblebees typically nest in the ground.

Male carpenter bees are quite aggressive, often hovering in front of people who are around the nests. The males are quite harmless, however, since they lack stingers. Female carpenter bees can inflict a painful sting but seldom will unless they are handled or molested.

Carpenter bees overwinter as adults in wood within abandoned nest tunnels. They emerge in the spring, usually in April or May. After mating, the females dig tunnels in wood and lay their eggs inside the tunnels. The entrance hole and tunnels are perfectly round and about the width of your finger.

Carpenter bees prefer to attack wood which is bare, weathered and unpainted. The best way to deter the bees is to paint all exposed wood surfaces, especially those which have a history of being attacked. Wood stains and preservatives are less reliable than painting, but will provide some degree of protection versus bare wood.

Liquid sprays of carbaryl (Sevin), chlorpyrifos (Dursban), or a synthetic pyrethroid (e.g., permethrin or cyfluthrin) can be applied as a preventive to wood surfaces which are attracting bees. These sprays usually only last for 1-2 weeks, however, and the treatment may need to be repeated. Tunnels which have already been excavated are best treated by spraying an insecticidal dust (e.g., 5 percent carbaryl) into the nest opening. Leave the hole open for a few days after treatment to allow the bees to contact and distribute the insecticide throughout the tunnels. Then plug the entrance hole with a piece of wooden dowel coated with carpenter's glue, or wood putty. This will prevent the bees from reusing the tunnels and also help against wood decay.

Although carpenter bees are less aggressive than wasps, female bees provisioning their nests will sting. So, if you're going to treat your wood, it's best to do it at night when the bees are less active.