Carpenter bees (Fig. 1) can be a serious pest on outdoor structures made of wood, such as patios, decks, sidings of homes, sheds, furniture, etc. Large carpenter bee, Xylocopa virginica is the most common species found in Georgia. Adult carpenter bees are pollinators, but mated females bore tunnels into wooden structures to rear their larvae. This process can cause substantial damage to the wood. With much tunneling, the integrity of the structure is compromised. Carpenter bees are more attracted to redwood, cedar, cypress, and pine, especially when old and unpainted. The body of a carpenter bee is metallic black in color with a glossy and hairless abdomen (Fig. 1). Bumblebees, on the other hand, look similar to carpenter bees, but the abdomen of bumblebees is hairy with yellow and black stripes (Fig. 2). Bumblebees do not use wooden structures to build their nest; instead, they build their nests in the ground using abandoned rodent burrows, totally in contrast to the carpenter bee nesting habit. It’s important to distinguish between the two, as the threat posed by carpenter bees is unique and requires specific preventative measures.
Biology and lifecycle
Life stages of carpenter bee include egg, larva, pupa, and adult (Fig. 3). Unlike bumblebee and honeybee, which are social, carpenter bee is not a social insect. Carpenter bee does not live in colonies with workers, drones, and queens. Carpenter bee is solitary, meaning one adult is in each nest, and eggs or larvae develop inside the nest. Adults of carpenter bee singly overwinter from November to February. An adult carpenter bee moves into the existing tunnel their parents bore in the spring and summer for overwintering (Fig. 4). The females and males emerge from those tunnels in February. The emerged bees mate. Mated females bore tunnels into the wood (Fig. 5). From March to April, females singly lay eggs in compartments or cells once the brood tunnel is completely drilled. The depth of the tunnel varies. During egg laying, females forage pollen and nectar from immediate landscapes to provision food (as a ball) in each cell near those eggs. Once an egg is laid and provisioned, it builds a wall using wood pulp and regurgitates to form a cell. Adults also feed on pollen for their energy needs. Males guard the nests to prevent multiple females from entering the nest and utilize the tunnel to lay eggs. Once the egg-laying is completed, the females die off. Eggs hatch by March and larvae gradually grow by molting from one stage to another, feeding on the food ball prepared by females within each cell. They pupate inside the cells, and by August, new adults emerge from those tunnels (Fig. 5). These new adults move out of nests to forage and feed on pollen and nectar from various floral resources from the late summer to fall to develop their nutrient reserves to survive the winter. Those new adults move into pre-existing brood tunnels as temperatures reduce in the fall (in November). They overwinter in those tunnels and then emerge from the tunnels in February of the following year to continue the cycle.
Damage
Females bore into the wood, leaving round-shaped ~1 cm-diameter (0.39 inch) entry holes (Fig. 6A). As they bore, they push out sawdust near the entry hole (Fig. 6B) and do not feed on wood. The boring activity produces sounds that can be heard coming from the wood. Although they make perfect entry holes, they bore along the length of the wood after a short perpendicular hole. Sometimes, females reuse old tunnels repeatedly every year. Repeated tunneling on the same wood for many years can compromise the structure’s integrity.
Although carpenter bees fly around aggressively during mating, constructing, or guarding the nest, they rarely attack humans or animals. This is especially true for males, who have no stingers. One of the important predators of carpenter bees is woodpeckers (Fig. 7). They are especially attracted to carpenter bees when they actively bore the wood as the boring process produces a unique sound. Woodpeckers can break the structure and cause structural damage as they try to access the adult females and larvae developing in the tunnels.
Management
Carpenter bee traps
Installing traps near carpenter bee activity, such as patios, porches, decks, sheds, barns, or houses, can reduce their population. Many traps are available (Fig. 8), which can be purchased from local garden stores or online. Female carpenter bees naturally explore existing entry holes, and this behavior is utilized in most traps (Fig. 8A). Once entered, females are trapped in a plastic bottle or box with restricted passage to return. Females do not bore through plastic, metal, or glass material. The trapped carpenter bees die within the collection container. Sticky traps can also effectively capture carpenter bees (Fig. 8B); however, they will have bycatch, such as paper wasps, etc.
Physical control
Carpenter bees can be physically removed using netting or swatting with a flat bat. If this approach is followed through consistently, some adults could be eliminated.
Plugging entry holes
Search for entry holes on wooden structures, and once found, plugging those holes may reduce repeated use of the same nests. The entry holes can be plugged by hammering a wooden dowel into the entry hole and coating it with sealants, such as glue, putty, etc. Females inside the nest will not bore an exit hole if trapped due to plugging. Severely damaged wood may need to be replaced, especially when the wood that supports the structure is seriously damaged.
Cultural control
Although the effects of paint and staining are poorly understood, anecdotal observations indicate that they avoid painted wood (oil-based paint) for nest building. Securing some wood structures, such as pieces of furniture, indoors can reduce the boring damage. Keeping outside doors shut, especially in the early spring, will reduce access to wooden structures from entry holes.
Chemical control
Insecticides can be used to prevent the completion of nest construction. Pyrethroid insecticides are effective and can be sprayed directly into the entry hole. Dust formulations of insecticides are also effective in reducing the carpenter bee problem. Once an insecticide is applied, the bees will spread the insecticide residues inside the tunnel as they move in and out. Thus, leaving the tunnel open for a couple of days after the insecticide application will increase the effectiveness of the applied insecticide. After one or two days, the holes can be plugged. The residual activity of pyrethroid insecticides will not last more than four weeks; thus, repeated application might be necessary in some cases. If a high activity of carpenter bees is anticipated in an area, these insecticides could be sprayed on the structure before the females’ boring activity begins in the spring. Again, the insecticide residue on the surface will lose efficacy within a few weeks, and reapplication is needed. The downside of this approach is that getting good insecticide coverage on the surface of the entire vulnerable structure is challenging, especially if it is large, such as a deck or a house. Wear proper PPE (personal protection equipment), such as gloves, long-sleeve shirt, etc., as recommended on the label before applying insecticide. Pay attention to the direction of the wind to prevent exposure. Because carpenter bee damage could be in areas of wood structure typically out of sight and unreachable, seek appropriate support. For professional applications, pest control companies are equipped to reach damaged areas of the structure.
References
Balduf WV. 1962. Life of the carpenter bee, Xylocopa virginica (Linn.). Annals of the Entomological Society of America 55: 263-271.
Jones, S. C. 2017. Carpenter bees. Department of Entomology, The Ohio State University. https://ohioline.osu.edu/factsheet/hyg-2074
Hurd PD Jr. 1958. Observations on the nesting habits of some new world carpenter bees with remarks on their importance in the problem of species formation. Annals of the Entomological Society of America 51: 365-375.
Potter, M. 2018. Carpenter bees. ENTFACT-611 https://entomology.ca.uky.edu/ef611
Sabrosky CW. 1962. Mating in Xylocopa virginica. Proceedings of the Entomology Society of Washington 64: 184.
