Have you seen large black or golden-brown bees foraging in your garden? These could be carpenter bees. Carpenter bees bore into lumber or trees to make nests for their brood and can damage structural wood or leave unsightly holes and stains. Multiple bees may use a common entry hole, tunneling several feet into wood to create chambers for their offspring, and the sound or sight of these large bees may be disturbing to some people. However, carpenter bees are considered mostly beneficial because of their role in pollination. Males can't sting and females rarely do.
Female mountain carpenter bee.
Prevention is the best approach for management. Use hardwoods in structures where possible and paint or varnish exposed surfaces. If you find carpenter bee holes and nests in your structure, wait for bees to emerge and fill the holes
with steel wool or caulk to prevent their reuse. Pesticides should not usually be necessary. Read more about these insects in the newly revised Pest Note: Carpenter Bees.
Male valley carpenter bee.