Although we may love them with all our hearts, it is true that every one of our most beloved friends and family have sides that at times make us mad… and that’s no reason for us to love them less. I feel our relationship with pollinators and other beneficial insects is similar to that which we have with our loved ones: pollinators pollinate and play an important role in native plant reproduction and food production… and sometimes can become a nuisance if not properly managed. As for our loved ones, the fact that pollinators can become a nuisance shouldn’t stop us from supporting them; we just need to learn how to sustain our relationship while controlling its negative aspects. In today’s post we’ll talk about one pollinator in particular, with which our relationship can sometimes become complicated. Let’s talk about carpenter bees.
What are carpenter bees?
In our area, carpenter bees are large bees belonging to the bee genus Xylocopa. If you enjoy being outdoors, I am pretty sure you have already seen them. A very common species in our region is the eastern carpenter bee, which is about the size of a bumblebee, has a “dot” on its back and dark wings, and when exposed to the sun, has a shiny abdomen. These bees are very common in our area, and are very regular floral visitors of many ornamental and food-producing plants.
The eastern carpenter bee (left), a native to the mid-Atlantic, has a shiny abdomen, while bumblebees (right) have fuzzy and hairy abdomens. Photos: J. Gallagher, Wikimedia: R. Hodnett.
Because they are about the same size as bumblebees, carpenter bees are often confused with them. To differentiate them, a look at their abdomen will quickly allow us to know who’s who; carpenter bees have shiny abdomens, while bumblebees have very fuzzy and hairy abdomens.
The life cycle of a carpenter bees
It’s not random that carpenter bees are called that way. Their life cycle is tightly linked to wood, in which females dig holes to build their nests. Carpenter bees have impressive mandibles that they can use to chew soft wood to dig galleries in it. Although they may seem impressive, these are peaceful bees that sting only if physically and aggressively disturbed. In the spring, males of these bees establish and defend their territories, a strategy that will win them a female to mate with. During this defense, they “chase away” other males but also people who may be close to what they consider their spaces. These males are harmless, however, since they have no stingers and thus can’t sting.
The life cycle of these bees goes hand-in-hand with the season. In the early spring the hibernating adults emerge, mate, and the females build their nests in the wood. These nests consist of galleries, at the end of which the females lay eggs and store food (nectar and pollen) for the developing larva. The larvae develop throughout the spring and summer, and by the end of the summer emerge as adults. These adults are the carpenter bees we usually see flying in the early fall. Once the weather starts becoming chillier, at the beginning of the winter, these adults return to some of the cavities and overwinter there, emerging the following spring, to restart the cycle.
Why can carpenter bees become a nuisance?
As we saw above, carpenter bees nest in wood. If a house or any structure is built of wood, they may pick it to build their nests. When this happens, these bees have the potential to affect the integrity of our wooden buildings. So, we see that while these bees are very important pollinators native to our region, this particular aspect is the one that can be problematic in our relationship with them. The good news is that there are solutions for this!
If there are no nests yet in the wood
The best solution is of course not the reactive, but the proactive one. If we have important wood structures that we don’t want to see occupied by these bees, the best we can do is first to use hardwood (which these bees tend to dislike) and/or to treat the wood. The treatment consists in painting or varnishing the wood, which will deter the adults from nesting in it. A very good treatment is coating the wood with almond oil in the spring, which will deter the bees from choosing that section to nest.
Another proactive action that can be taken along with wood staining is to distract the bees from the wood that we want to protect. To do this, one can use pieces of wood that one may not be interested in keeping, and displaying them in other parts of the open spaces so that females choose to nest in those surfaces instead of in the wood we want to protect. Besides protecting the wood, this also allows us to support these important native pollinators from our region, all while reducing the potential negative impacts on our buildings.
If bees are already established in the wood
If carpenter bees are already established, there are several options. First, if the number of nests is really low, and if the structure can be removed and replaced, then this should be done and the new wood structure should be stained to protect it. If possible, the piece of wood that is removed can then be placed elsewhere in the green spaces around the property, which will provide nesting resources for this pollinator, and will simultaneously protect the house and support native pollinators.
If the piece of wood can’t be removed and, in particular, if the nests appear to jeopardize the integrity of the building, a more radical action should be taken. In that case, the use of insecticides can be considered. If this path is taken, it is important to not perform insecticide applications without proper knowledge, meaning that this should be done by an expert applicator. This point is really important, because non-targeted and improper insecticide treatments can lead to a lower efficiency of the treatment on the carpenter bees, and the death of other non-target beneficial insects (e.g., other bees, beneficial pest control insects, etc.) that may become in contact with the treated region.
By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.
Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!
I am glad you addressed preventative and remedial measures, but given the damage they do, I think it is fair to go another step and say we can do without them. Let’s instead take measures to promote other bees that aren’t destructive. I compare carpenter bees to pitbulls which are loved companions to some, but have also caused a grossly disproportionate amount of injury and death vs. other species. There are plenty of other dogs to choose from so why accept such a dangerous breed. Ditto your bees.
Anahí, I’ve been happily hosting carpenter bees in my split rail fence for years. Now my neighbors have put up their own wooden fence next to it, and it doesn’t make sense to have two fences. I thought of waiting a year to allow the bees to begin transferring over to the new wood, and then removing my fence when all larvae have emerged next fall. Does this timing sound right to you?
To George Lambert I say: pitbulls are a breed of dog artificially created by humans, with no particular role in the natural world. Carpenter bees are a naturally occurring part of the web of life, with a distinct role to play. There is no equivalence.
IDA, the “natural world” has many components that are neither benign and/or beneficial. Let’s consider mosquitoes, lanternflies, rats, mice, moles, ticks, etc., not to mention Covid, floods, hurricanes and tornadoes. Carpenter bees also belong on that list. It is the same as deer which if away from mankind are fine, but if near us without predators are destructive and dangerous. If Mother Nature dishes up a fungus or bacteria that destroys concrete, should we just say c’est la vie? Arsenic, radon and carbon monoxide are also natural, but not recommended for our backyards.