Carpenter bees are large, black and yellow bees often seen hovering around the eaves of houses, wooden fences or underneath a deck in late spring. They look like bumblebees but have a black shiny tail section.

Wooden decks and overhangs are a major target. Painted surfaces are less preferred but can still be damaged. Unpainted or stained cedar, cypress and redwood shingles and siding are also attacked.

The carpenter bee bores a round, one-half inch entrance hole in the wood. Occasionally, several bees may use the same entrance hole and have individual branches off the main tunnel. Carpenter bees differ from termites in that they do not consume the wood as food. They are excavating tunnels for nesting sites.

Carpenter bees overwinter in the tunnels. They emerge in the spring, usually in April or May. They feed on plant nectar and then start building new tunnels. The females drill tunnels in which they build a large pollen ball and then lay eggs. Finally they seal off the section of tunnel containing the pollen ball and eggs. Males are very territorial and will harass people who come near their protected area; however, they do not sting. These adult bees die in a few weeks, and the eggs hatch a few days later.

Carpenter bees do not cause serious structural damage to wood unless large numbers of bees are allowed to drill many tunnels over many years. Woodpeckers may damage infested wood looking for bee larvae in the tunnels and this damage can be severe.

Treat entrance holes with an insecticidal spray or dust to reduce carpenter bee activity. Products containing carbaryl (Sevin), cyfluthrin or resmethrin are suitable. Always follow the manufacturer’s recommendations for application rates and safety precautions. After plugging the holes with one of the recommended insecticides, fill the holes with wood putty. The insecticide treatment should kill both the adult bee and its offspring as they emerge later. Spraying bees seen hovering around is not a sensible use of pesticides. You might accidentally kill honey bees which are beneficial insects.