Accompanying the arrival of spring are the various bees and wasps that hover erratically—sometimes in large numbers—around homes and other wooden structures. Residents are often are intimidated and frightened by these pesky yellow and black bees because they may sting.
Among the flying bees and wasps are the large black and yellow colored carpenter bees. Adult carpenter bees, both female and male, spend the winter hibernating inside old nest tunnels. Overwintered adult bees emerge in early spring to mate and search for nest sites. They remain very active through the summer. They earn their name because they bore 1/2 inch-wide holes that appear to be perfectly round on exterior wood surfaces.
Carpenter bees are good pollinators and naturally nest in dead trees and woodpiles, but they have taken up residence in close proximity to human habitation and cause extensive damages to wood structures, including homes, when they repeatedly colonize exposed wood and they are not controlled. Additionally, woodpeckers feeding on the developing bee larvae will tear into the galleries, further damaging the wood to the point where it needs replacing.
Female carpenter bees are the one causing the damage. In order to lay eggs, females drill into dry wood on in home buildings—such as siding, fascia boards, porch window trim, porch ceilings, fence, decks, outdoor furniture and other wooden surfaces. The female chews a perfectly round entrance hole about the size of a dime, directly into the dry wood about an inch, then turns a 90-degree angle to excavate a tunnel (or gallery), usually along the grain of the wood. Inside each gallery, the female constructs 6 to 14 cells. In each cell, the female privations a ball of mixed pollen and nectar, lays an egg on the ball, then seals off each cell with chewed wood pulp. The eggs hatch and the larvae (grub stage) develop into adult, which chew through the cell partition and emerge in late summer.
Gallery construction is a labor-intensive process, so females often prefer to use old galleries for the next generation. Usually the gallery will extend about 4 to 6 inches, but with repeated use the galleries can be up to 2 feet long. Therefore, if you had carpenter bees last year, you will likely have them again this year.
Signs of Carpenter Bee Infestation
- Carpenter bees hover nearby and around your building and structures. They are looking for nesting sites to born in.
- Coarse sawdust that collects beneath excavated cavities during the spring.
- Round and smooth holes, in size of a dime, on exterior wood surface
- Unsightly stains caused by falling bee waste around the round-entrance hole
- You may also notice a buzzing or burrowing sound coming from within the wood.
Do carpenter bees sting?
Carpenter bees are very unlikely to sting people. Females have a stinger but are not defensive unless being directly provoked.
Males do not have a stinger, but they intend to be territorial and protect the female and the nest. The carpenter bees hovering nearby or buzzing around people when being approached are most likely males that are putting on a territorial show of aggression. But don’t worry, males do not have a stinger, making them harmless.
Males have a white or yellow blaze on their face, while females have a dark face.
How to tell carpenter bees from bumble bees?
Carpenter bees resemble bumble bees, both have a robust plump body and larger than other bees. There are two species of carpenter bees in the eastern United States and three more in the western United States. In order to thrive, they need an environment of blooming landscape and available structural timbers, as well as dead wood to nest in. In Alabama the most common species of carpenter bee is the Xylocopa virginica.
A quick and simply way to tell them apart is by looking at its abdomen. The abdomen of carpenter bee is shiny black and hairless; while the bumble bee’s is covered with soft/fuzzy hairs patterned with distinct black and yellow stripes.
They behave differently.
- Carpenter bees are solitary bees and less defensive of their nest sites. Bumble bees are social and extremely defensive when their nest site is disturbed.
- Carpenter bees tend to stick closely to their preferred wooden environment. Bumble bees are likely found around blossoming plants and flowers.
- Carpenter bees fly in a more erratic way, like chasing one another rather than fly together in harmony. Bumble bees fly leisurely together.
- They inhabit differently. Carpenter bees carve their own tunnels and nest above-ground wood materials. Bumble bees lives in social colonies usually nesting in the ground.
Early spring is the best time to treat and/or seal those openings on wood surface. Timing is important because the goal of carpenter bee control is to deter the nesting damage but not eliminate all of the bees in the yard since they are important pollinators. The best time is before the female lays eggs in the tunnel. Products with essential oil components can repel carpenter bees from carving tunnels or abandoning the excavated nest.
A painted surface is a deterrent to carpenter bee activities. Unfortunately, painting or placing polyurethane on wood decks or log homes is often not a desirable option. Wood stains provide little repelling action.
If practical, severally damaged wood should be removed and replaced with chemical pressure-treated wood to prevent nest construction. Consider use of synthetic sidings rather than wood sidings.
Sometimes it is necessary to control carpenter bees causing damage. Simply sealing the entrance holes with caulking or expanding foam does not work if the holes are not treated with a pesticide. The trapped adult carpenter bees can chew through caulk escaping or excavate new openings. Commercial and homemade traps can catch carpenter bees if properly installed but often do not provide effective control around a structure.
There are insecticide products commercially labeled for carpenter bee control and can be applied to exposed wood and gallery entrances. These products are formulated for dusting, aerosol, forming and liquid sprays. Each formula has its pros and cons. Sprays can be the easiest to apply, but too much spray may soak the raw wood. Aerosol sprays, especially foaming formulations with a straw attachment, can be effective if applied to each hole, but overuse can also get the chemical soaked into raw wood over time. Dusts applied to each hole will stay on the surface and can be effective, but dusts can be messy to apply without appropriate applicators.
No matter which product is used, all label directions must be followed. Application should be done late in the evening when the female bees are most likely to be inside the wood tunnels and less active. Additionally, it is always a good idea to wear a long-sleeved shirt, chemically resistant gloves, and protective eyewear when making applications to reduce the chance of a sting.
After applying an insecticide, the tunnel entrances should be plugged using Trebor plug, Super Plug or wood patch material to stop other insects from invading the hole at a later time.
It can be very challenging to reach many of the holes the bees are using. However, if holes are not treated and plugged, the carpenter bees will probably continue to reuse the same hole every year. Consider hiring a pest management professional with the experience and equipment needed to make an effective and safe application.