Carpenter bees can be a nuisance to homeowners, thanks to their habit of tunneling into decks, porches, and other wood structures. Males behave aggressively during their spring mating season, which can be a bit unsettling if you're trying to relax on your deck. Your first impulse might be to grab a can of bug spray to battle these large bees, but please don't. Learn when control measures are needed and when they aren't, and how to control carpenter bees effectively.
What Are Carpenter Bees?
People often mistake carpenter bees for bumblebees, which look quite similar. Bumblebees (genus Bombus) nest in the ground, usually in abandoned rodent nests, and live in social communities. Carpenter bees (genus Xylocopa) are solitary bees that burrow into wood. If you see a bee that looks like a bumblebee emerging from a hole in your porch, it's a carpenter bee, not a bumblebee. You can differentiate the two by examining the dorsal (upper) side of the abdomen. If it's shiny and hairless, it's a carpenter bee. A bumblebee, by contrast, has a hairy abdomen.
Carpenter bees usually spend the cold months tucked inside their empty nest tunnels, protected from freezing temperatures and winter weather. In spring, they emerge ready to mate. The female carpenter bee excavates a tunnel for her offspring. In each brood chamber, she stores food and lays an egg. By late summer, her young emerge as adults. The new generation of carpenter bees will visit flowers briefly in August and September, before settling in for the winter.
Carpenter bees are excellent pollinators. When a carpenter bee lands on a flower, she vibrates her thoracic muscles to shake the pollen loose. Because carpenter bees are beneficial insects, you should only eliminate them when necessary.
Do Carpenter Bees Sting?
Most people encounter carpenter bees during April and May, when they've just emerged to mate. During this time, male carpenter bees tend to hover around nest openings, looking for receptive females. It can be rather unnerving being around them, as the males will also hover aggressively around people who approach the nests. They may even fly right into you. Despite this tough act, male carpenter bees cannot sting. They are completely harmless. Female carpenter bees can sting, but almost never do. You would have to provoke a female, perhaps by trying to cup her in your hands, to get her to sting you in self-defense. So carpenter bees pose almost no threat to people at all.
How to Identify Carpenter Bee Nests
Obviously, if you observe carpenter bees coming and going from holes in your fascia board, deck posts, or other wood structures, that's a sure sign that those holes are carpenter bee nests.
If you haven't seen bees, but suspect they may be burrowing in a fence or other structure, look at the entrance holes. A carpenter bee makes an entrance hole slightly bigger than her body, or just about ½ inch in diameter. The first inch or two of the tunnel is usually made against the wood grain. The bee will then make a right turn and extend the tunnel another 4-6 inches in the direction of the wood grain. Carpenter bees will often eliminate their waste before entering their nest, so you might see yellow stains on the surface of the wood, just below the entrance hole.
Though they burrow into wood, carpenter bees don't eat wood like termites do. Since their nest tunnels are limited in size, they rarely do serious structural damage. However, because such excavation requires a lot of energy on her part, a female carpenter bee will often prefer to refurbish an old tunnel to digging a new one. If carpenter bees are allowed to tunnel in the same structure year after year, the cumulative damage could be significant.
How to Control Carpenter Bees
When it comes to carpenter bees, your best defense is a good offense. Carpenter bees prefer to excavate untreated, unfinished wood. You can discourage, if not prevent, carpenter bees from nesting in a wood structure by painting or varnishing the lumber.
If carpenter bees are already a problem, you will need to use an insecticidal dust to treat the nests. Insecticidal dusts are usually applied with a puffer that allows you to coat the interior surface of the entrance holes with the insecticide using a gentle burst of air. Contact your local extension office to find out which insecticides are effective and legal for use on carpenter bees in your area.
For the insecticide to work, the bees much come in contact with it as they crawl through the entrance hole of the nest. Apply the appropriate insecticidal dust in the spring, just before adults emerge to mate. Once you see the bees emerge, wait a few days before filling in the nest holes with wood putty or filler.
If you didn't apply the insecticide before the spring adults emerged, you will need to treat the nests twice – once in the spring, and again in late summer, when the next generation of adults is foraging. Because bees will be active during the day, it's preferable to apply the pesticide at night. This will reduce your chances of being stung by females trying to defend their nests. In the fall, seal the nest holes with putty or filler.
- NCSU Entomology Insect Notes – Carpenter Bees, accessed April 2, 2012
- Carpenter Bees— Penn State University, accessed April 2, 2012
- Carpenter Bees Management Guidelines--UC IPM, accessed April 2, 2012
- G7424 Carpenter Bees - University of Missouri Extension, accessed April 2, 2012
- Carpenter Bees, HYG-2074-06, accessed April 2, 2012