Cover Story
CARPENTER BEES: Uninvited Houseguests Who Do Not Take a Hint
By Dr. Jennifer Tsuruda, Assistant Professor, and Dr. Karen Vail, Professor, UT Entomology and Plant Pathology Department
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pring is here, and as floral resources become abundant, bees begin buzzing and developing their nests. Most people who spend time outside are familiar with large carpenter bees (Xylocopa species) – their size, loud buzzing, and hovering make them hard to miss. While the behavior and activity of these native bees can be problematic for homeowners, these bee species also provide beneficial pollinator services.
How to Recognize Carpenter Bees • Large bees, 0.75" (20 mm) or more in length • Dark/black abdomen [Photo 1] o Carpenter bees are similar in appearance to bumble bees [Photo 2] o The adult abdomen is less hairy than bumble bees o Carpenter bees have a “shiny hiney”, with little to no hair [Photo 1] • Light patch on the “face” of males [Photo 3] o Males cannot sting but can appear intimidating when hovering around people near nesting sites or females • Xylocopa virginica and Xylocopa micans both occur in Tennessee. Other species may be present in other regions
Reproductive Habits and Resource Use Rather than living in colonies, like honey bees and bumble bees, female carpenter bees create nesting galleries in wood. Carpenter bee entrance holes excavated by females are very clean and circular, around ½" (12 mm) in diameter [Photo 4]. From the entrance hole, the colony-founding female will turn and chew one or more tunnels that are often 4 – 7" long, but can extend several feet after reuse and expansion over multiple years.
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tennessee greentimes SPRING 2022
A tunnel consists of a series of cells, each provisioned with a ball of pollen mixed with nectar, and a single egg [Photo 5]. Each cell is sectioned off with a division of chewed up wood pulp. After hatching, the larva consumes the provisions and progresses through multiple larval instars before pupating into an adult. Adults emerge in the summer and forage on floral resources before overwintering in galleries. In the spring, males typically emerge earlier than females and establish and guard territories and females. Given the overlapping housing issues for humans and carpenter bees, many homeowners are surprised that carpenter bees can still be considered beneficial insects for their ecosystem services [Photo 6]. Native bees, including carpenter bees, pollinate approximately 15% of agricultural crops in the US. Carpenter bees are also frequent pollinators of home gardens that include tomatoes, eggplants, and other plants needing sonication for the release of pollen (buzz pollination). General preferences for carpenter bees include unpainted, untreated, weathered wood from varieties of softwood trees, like cedar, spruce, and pine, that are easier to chew. However, lumber from less preferred hardwood species may be utilized if these are the only available resources. Carpenter bee galleries in natural wood can be found in stumps, logs, and dead branches. Structural lumber and fence posts are timber products that are frequently compromised.
Carpenter Bee Damage and Management While carpenter bees contribute valuable ecosystem services as pollinators, they also are often considered pests. Our annoyance also stems from sustained infestations, repeated fly-by’s and buzzing, and defecation streaking below nest entry holes [Photo 7]. A single year’s nest building may not result in extensive damage, but carpenter bees continue to expand upon old nests, adding additional galleries in subsequent years. In time, their activity can weaken structural timbers if not curtailed. Successful management often requires multiple actions, repeated treatments, and persistent efforts.
