Male and female carpenter bees are becoming active after spending the winter in last year’s tunnels. They resemble bumble bees but have shiny, bare abdomens (Figure 1); 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 faces, hang out near nesting sites and may investigate intruders who enter “their” space. While intimidating, they do not have stingers.
Carpenter Bee Tunnels
Females use their strong mandibles to chew 1/2-inch diameter entry holes into soft, dry wood (Figure 2). Tunnels follow the grain and are become about 1 inch longer each week. Ultimately, tunnels can be 6 to 10 inches long and can contain 6 or 7 individual larval cells. Each cell 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 tunneling can become extensive over time. However, woodpeckers can cause much more damage as they hammer at bee-infested wood to feed upon developing bee larvae (Figure 3). Reducing carpenter bee attack and plugging entry holes with sections of dowel rod should stop woodpecker visits.
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 metal window screen will prevent injury to areas that are chronically attacked. Closing barn and shed doors while 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, sanding surfaces so they are smooth, and painting or varnishing exposed wood will make these areas less attractive.
Carpenter bees are searching for ½-inch diameter entry holes to use for nesting. This can be exploited through the use of carpenter bee or wood bee traps; search the Internet for those key words to obtain design ideas.
There are some insecticide options but accessibility and dimensions of infested surfaces can make treatment impractical or limit 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. Examples of 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.
By Lee Townsend, Extension Entomologist