Carpenter bees (Figure 1) are beginning to buzz about after spending winter as adults in the tunnels where they were raised last summer. After mating and a little spring cleaning, females will re-use their “home tunnels” (Figure 2) while the others will have to to find new sites. Carpenter bees usually do not venture far, so many tunnels can appear in suitable wood over several years.
Carpenter bees chew ½-inch diameter tunnels that follow the wood’s grain. Females may use their strong mandibles to extended the galleries by more than ½-inch per day. After construction, females spend much of May gathering pollen and nectar that is fashioned into bean-sized portions of bee bread. The female will deposit an egg on each “loaf” and separate them into cells.
Tunneling in soft wood is the main damage inflicted by carpenter bees. Over time, increasingly larger carpenter bee populations can weaken wood. In addition, the accumulating waste from the bees stains surfaces directly below nest openings.
Damage becomes significantly worse if woodpeckers discover carpenter bee galleries. These birds will destroy wood to reach the succulent bee larvae just below the surface (Figure 3).
Finally, the buzzing of these intimidating bees can stress those that live or work around the structures used by carpenter bees as nesting sites . Females are not aggressive but can give a painful sting if antagonized. Males, recognizable by the yellow spot on their faces (Figure 4), hang out near nesting sites and may investigate intruders who enter “their” space. While intimidating, males do not have stingers.
Carpenter bee control is not easy, so prevention is the best long-term strategy.
- Use hardwoods (when practical), or cover softwoods with flashing or screen to prevent injury to areas that are chronically attacked.
- Close barn and shed doors while bees are establishing new galleries; this helps reduce infestations in outbuildings.
- General maintenance of wood helps because carpenter bees exploit rough areas on wood surfaces to begin a nest. Filling cracks and crevices, sanding, 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 bees may not pick-up of the dried residue as rapidly as they would 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), and 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