Male and female carpenter bees are becoming active after spending the winter in old nest tunnels. They resemble bumble bees but have shiny, bare abdomens; bumble bee abdomens are “hairy”. Females have black faces. They are not aggressive but can give a painful sting if antagonized.
Males, recognizable by the yellow spot on their face, hang out near nesting sites and may investigate intruders who enter “their” space. While intimidating, they do not have stingers.
Females use their strong mandibles to chew 1/2-inch diameter entry holes into soft, dry wood. Tunnels follow the grain and are get about 1 inch longer each week. Ultimately, they can be 6 to 10 inches long and can contain 6 or 7 individual larval cells. Each is provisioned with a ball of nectar and pollen as food for the grub-like larva. Over the years, galleries may become several feet long.
Carpenter bee control is not easy, so prevention is the best long term strategy. Use of hardwoods when practical, or covering softwoods with flashing or screen will prevent injury to areas that are chronically attacked. Closing barn and shed doors while the bees are establishing new galleries should help to reduce infestations. General maintenance helps because carpenter bees exploit rough areas on wood surfaces to begin a nest. Filling cracks and crevices and painting or varnishing exposed wood will make it less attractive.
There are some insecticide options, but accessibility and dimensions of infested surfaces can make treatment impractical or limit its success. The use of dust formulations of insecticides applied directly into tunnel openings has been the favored option. In this approach, bees are exposed to the dust as they enter and leave. Ultimately, they should receive a lethal dose. Example dusts include boric acid dust, or products such as Bonide Termite & Carpenter Ant Dust (deltamethrin). Diatomaceous earth and combinations of dusts with desiccants are also possibilities.
Insecticide sprays can be applied into tunnels, but pick-up of the dried residue may not be as rapid as with dusts. Insecticide applications to wood may provide some preventive effect, but bees are not ingesting the wood, only gouging it away; they can work quickly though the treated surface. Example sprays include Bayer Home Pest Control Indoor & Outdoor Insect Killer (cyfluthrin), Bonide Total Pest Control Outdoor Formula (permethrin), Bonide Termite & Carpenter Ant Killer Ready to Use (deltamethrin), Spectracide Bug Stop (l-cyhalothrin). After treatment, tunnel entries should be filled and sealed so they are not attractive to bees next season.
By Lee Townsend, Extension Entomologist