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Bruce Johnson

Author, Columnist and Director of the
National Arts & Crafts Conference
at The Grove Park Inn since 1988

Arts & Crafts Furniture & Homes Help, Tips and Advice

Besieged By Carpenter Bees?

Besieged By Carpenter Bees?

April showers may bring May flowers, but with the flowers also come the drone of carpenter bees boring holes into the underside of our decks, railings and rafter tails.

Carpenter bees look nearly identical to bumble bees, immediately begging the question: can they sting?

The male carpenter bees are very aggressive, often flying within inches of your face, but they cannot sting. The females, however, which are not as territorial nor as aggressive as the males, can sting, but only if you pick them up.

Tip of the Week: Don't pick them up.

Author Richard M. Houseman offers the following:

"Carpenter bees are normally considered to be beneficial insects since they pollinate a wide variety of plant species. However, when making tunnels in the wood of human structures, they are considered to be economic pests. The openings to these tunnels are a near-perfect circle measuring approximately 1/2 inch in diameter. The tunnel goes straight into the wood for a few inches before making a 90-degree turn and following the length of the wood. It is not unusual for several tunnels to extend out from a single opening.

"Female carpenter bees construct individual cells within each tunnel. Each cell contains one egg and enough food for a developing larva. To make the food, she collects pollen and mixes it with plant nectar to form a substance called bee bread. She places the food into the tunnel, lays a single egg on it, and builds a partition in the tunnel with cemented wood chips. She continues this process until six to ten cells are constructed.

"The lifetime of a carpenter bee, from egg to death, covers one year. New adult bees emerge briefly in August or September, feed and re-enter their galleries to pass the winter. In the spring those bees that survive winter emerge again in April, mate and produce a new generation. They reuse existing tunnels or build new ones in which to lay their eggs. These adult bees die in July, following mating and egg-laying. Carpenter bee activity begins again when their offspring have matured and emerge briefly during September. Infestations may persist for several generations over several years, with each generation lasting a full year.

"People may become alarmed when holes begin to appear in exposed wood. Unsightly defecation stains may also be present near the openings to carpenter bee tunnels. While carpenter bees attack many species of dried, seasoned wood, they seem to prefer softwoods such as pine, fir, redwood and cedar. They prefer unpainted or well-weathered wood to painted or hardwood timbers. Preferred nesting sites are usually at least two inches thick.

"Management of carpenter bee populations consists of treating each individual tunnel opening with insecticide. Tunnel openings should be treated after dark when the bees are calm and in the nest — preferably on cool nights. Use a pressurized can of bee or wasp spray that shoots a stream of liquid into the tunnel and immobilizes the bees.

"Within a few days after treatment, tunnels can be filled with caulking compound, plastic wood or a tight-fitting (1/2-inch) wooden dowel glued in place. If paint on the wooden surface is not undesirable, painting will discourage further attack by other carpenter bees.

"Consider treating tunnel openings in the early spring before bee activity begins. Spring treatment is best and most effective before mating and egg-laying activity begins. When you treat tunnel openings before activity begins, wait until the bees have become active for a few days before you fill the tunnels.

"If mating, tunneling, and egg-laying activities have already begun in the spring, you will need to treat the tunnel openings at least twice. The first treatments occur during the spring activity period. These treatments eliminate the adults that are mating and building new nesting sites, but may not affect the eggs and larvae that are already developing inside the brood chambers.

"A second treatment can be made to the tunnel openings during the late summer activity period to ensure that adults that emerged from these larvae are also eliminated. Tunnels can be sealed after this second treatment."

- Bruce Johnson

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