Did you know that globally there is an excess of 20 000 bee species? Have you ever been out and about in the garden or on a lovely spring stroll in a meadow and suddenly been dive-bombed by a bee? Catching a glimpse of it, you thought it was a bumblebee. However, if you stopped to watch it for a few minutes, you might have discovered it was a type of wood bee. If you have no idea what we’re on about, read on because we’ll investigate wood bees in depth below.
Wood bees belong to the Xylocopinae bee subfamily and resemble bumblebees. They are found globally in tropical, subtropical, and temperate areas. The wood bees’ name comes from their making of nests in wooden structures, which is often seen as a problem. However, wood bees are important pollinators.
Although wood bees are often seen as pests, they are an essential component of the environment. But how do they contribute to ecosystem functioning? Where are they found? How do wood bees make their nests? What is their life cycle like? Do wood bees make honey? And can they sting you?
Bees species globally exceed the 20 000 mark, and within the United States, there are roughly 4 000 species of the little buzzers. The diversity in the US alone is considerable, as bees range in size, shape, behavior, and function in the environment.
Some bees are smaller (like the Perdita minima), while others (like the carpenter bee) are large (roughly 1 inch).
Although not all bees produce honey for “human consumption,” bees are beneficial and essential to the environment. Bees play a quintessential role in pollination, and without them, we’d lose most of our flowering plants (including our food species).
According to the USGS website, researchers estimate that native bees are responsible for pollinating up to 80% of the world’s plants. Wood bees, and other native bees, are responsible for roughly 15% of pollination in the US.
Wood bees are an essential part of many ecosystems. Below we will investigate their characteristics, distribution, behavior, and conservation.
Wood bees are also known as Carpenter bees. The name “carpenter bee” applies to numerous species of bees belonging to the Xylocopa (large carpenter bees) and Ceratina (small carpenter bees) genera. All carpenter bees belong to the subfamily Xylocopinae.
Globally, there are roughly 500 species of carpenter bee in the Xylocopa genus and roughly 350 species of the Ceratina genus.
The Ceratina genus contains 21 species within the US, while the Xylocopa genus contains 7 species.
They are the largest native bee species within the US and are similar in size to bumblebee queen bees.
In appearance, carpenter bees resemble bumblebees. Carpenter bees range from ¼ inch (in Ceratina) to 1 inch (in Xylocopa); they have 6 legs and prominent antennae.
However, carpenter bees lack the “fuzzy” appearance and yellow patterned abdomens that bumblebees exhibit and instead are smooth and shiny black. Their thoraxes are often solid or spotted yellow (especially the males).
Other colors include black, green-blue, metallic blue, or purple-blue.
With over 700 species, there is generally a fair amount of diversity in carpenter bee appearance (color and size). Still, they bear a general resemblance with their absence of hair on their abdomens. Female carpenter bees also have bushy hairs on their hind legs, while bumblebees generally have pollen sacks.
Carpenter bees are widely distributed globally, occurring on all continents except Antarctica and some polar regions. Carpenter bees usually inhabit tropical, subtropical, and temperate areas.
Within the USA, carpenter bee distribution includes the southern United States, from Arizona to Florida, and the eastern United States stretching northwards to New York.
The most common species of carpenter bee found in the US include:
- Xylocopa virginica and Xylocopa micans in eastern North America
- Xylocopa californica, X. tabaniformis, and X. varipuncta (X. sonorina) in western North America.
WoOD bees have various fascinating behaviors.
You might be wondering how carpenter bees got their name? Well, it’s a nickname they picked up for their habit of boring out perfectly rounded galleries inside wooden objects like dead trees, old stumps, fence poles, planks, rafters, etc. The small carpenter bee species (Ceratina spp.) make their nests in thinner stems of various plants (usually bushes).
Wood (carpenter) bees excavate these hollows by chewing their way into deadwood with their powerful jaws (mandibles). They don’t, however, occupy rotting wood.
Entomologists consider carpenter bees as solitary bees, and many are solitary, especially when nesting materials are in abundance. Although carpenter bees don’t live in mega hives, they exhibit a degree of social behavior. Newly hatched female bees often live with their mothers for two generations, especially when nesting materials are not abundant.
There even seems to be evidence of foraging bees returning to feed those bees which remain in the nest. The mother bee (queen) does all the work in these situations. She lays the eggs and collects the food while the remaining females (subordinate queens) defend the nest from other insects and opportunistic carpenter bees.
This excessive activity results in an elevated degree of “wear” on the queen’s body and reduces her lifespan to roughly 1 year. Once she dies, a subordinate queen takes her place, repeating the cycle.
Although carpenter bees exhibit rudimentary social behavior and colony dynamics, they lack the social structure and organization of honey bees, i.e., they don’t have a queen and infertile worker castes. All carpenter bees are fertile.
Breeding and mate selection within carpenter bees follows a “lek polygyny” system, whereby males defend an area with no particularly useful materials for nesting females. Males do not actively seek out females for breeding. Instead, the females seek out suitable mates, copulate, and leave.
Once the deed is done, the males return to the hovering defense of their site, awaiting the next female. Interestingly enough, males do not seem to return to the same area they defended the day before, opting to drift to other areas.
However, males of some species occasionally return to specific sites, but it is not a common trait.
Of special interest is the Xylocopa varipuncta carpenter bee. Green-eyed golden males congregate around non-flowering plants and release rose-scented pheromones from well-developed perfume glands in their thoraces.
These pheromones drift on the wind and attract nearby females, who then approach the group and select a mate.
Carpenter bees are generalist feeders, meaning they have no particular preference when selecting plants to feed on.
Carpenter bees generally forage early in the morning (another shared trait with bumblebees). Carpenter bees employ two distinct methods to obtain nectar and pollen when foraging.
Carpenter bees employ “buzz pollination.” When a carpenter bee forages from a flower, they emit ultrasonic vibrations (sonicate). These vibrations cause the flower’s anthers to release their pollen grains, which the carpenter bee collects.
The other fascinating method of foraging carpenter bees is “nectar robbing.” When carpenter bees visit flowers with long, tubular petals, their large bodies prevent them from reaching the nectar in flowers. In these situations, carpenter bees use their mouth to cut a small hole at the base of the flower (corolla) and suck out the nectar without collecting pollen from the flower.
Penstemons and salvias are examples of the flowers where carpenter bees become thieves.
On other flowers, carpenter bees use their tongues for drinking nectar in the “normal” way.
Spring is when carpenter bees are most active as they forage and look for mates. During the summer and fall, females continue collecting nectar and pollen, and over the winter, they usually hibernate.
Carpenter bees have stingers and, like most other bee species, will deliver a painful sting if provoked to the point of no other option. Important to note is that male carpenter bees lack stingers. They are, however, the bees you’ll find hovering around bushes or wood, divide-bombing intruders, as they defend their “territories.”
Females have smooth stingers, which means they could sting you repeatedly without dying (like honey bees). Fortunately, female carpenter bees are generally not aggressive and will only sting if you try to handle them or disturb their nests.
If you are stung, it’s important to remove the stinger immediately (if it is stuck in your skin). Once removed, you should wash the site with soap and water, but it would be wise to leave it alone. i.e., don’t cover it with anything (exposure to the surrounding air expedites the recovery process) or touch it unnecessarily.
Most often, a carpenter bee sting symptoms include pain and a burning sensation at and surrounding the site. If the site begins to swell, you can use an ice pack to control the swelling. If the pain persists, medication containing ibuprofen (e.g., Advil) or acetaminophen (e.g., Tylenol) will ease the pain.
In the worst-case scenario, you could have an allergic reaction to the venom, causing you to go into anaphylactic shock. You’ll need to get to an emergency room as quickly as possible in this dangerous situation.
Carpenter bees follow a similar 4-stage life cycle to other bees: egg, larva, pupa, and adult.
Avoiding the “who came first” argument, adult female carpenter bees lay roughly 6 to 10 eggs in their nests. These eggs take approximately 18 to 24 days to hatch.
Once the eggs hatch, white larvae emerge and feed on the “bee bread” deposited by the mothers.
Larvae grow for roughly 14/15 days, feeding on the honey and nectar provisions their mother left for them in the cell.
Once they’ve grown, the larvae rest for roughly 15 days as “pre-pupa.”
After the resting period is completed, the carpenter bee pupa is completely white, with a black spot on each antenna, but resembles adult carpenter bees.
Over time, the developing pupa resembles the adult coloration more closely. The carpenter bee undergoes a metamorphosis from larva to adult during this phase. This process takes roughly 36 days to complete (the time varies from species to species).
It takes roughly between 7 and 13 weeks for carpenter bees to transform from egg to adult.
At the end of its development, the newly formed adult breaks through the segregations within the brood chambers and exits the nest to feed.
Adults may return to their natal nest during the winter or find a new, unoccupied nest. Once winter passes, males mate with females and then die (males live for roughly 11 to 12 months), while some females lay eggs first and then die (roughly a little more than 1 year). However, some species live for up to 3 years (these are generally semi-social bees).
Good question! Bee bread is a concoction of bee saliva (and the enzymes present), nectar (sometimes honey, depending on the species), and pollen that bees collect and regurgitate to feed their offspring/hive mates.
Carpenter bee bread has a dough-like consistency, and they usually excrete it from their crop (where they store the nectar and pollen collected from plants).
Due to the pollen and nectar, bee bread is rich in carbohydrates, lipids, minerals, protein, and vitamins.
Carpenter bees don’t construct hives as honey bees do. Instead, they bore into wooden structures to create nests. Different species use different wooden items.
For example, the Xylocopa virginica carpenter bee of the eastern USA often chooses to move into fence posts and other timber, especially of redwood origins.
As a carpenter bee carves out its tunnel in the wood, they usually include a 90° turn after the first 2 inches of boring into the wooden structure. This turn allows the bees to follow the wood grain for between 6 to 8 inches. This tunnel then becomes the “brood chambers” that females segregate during egg-laying.
There are typically between 6 and 10 brood chambers per nest. Females build these wooden wall partitions by combining sawdust and saliva (these walls are a similar consistency to chipboard).
Starting from the deepest part of the tunnel (furthest from the entrance), the female lays an egg, closes off the cell, then lays the next and closes it off, working her way towards the entrance.
Females lay their gigantic (0.59inch) eggs on top of the “bee bread,” which eventually hatch into larvae.
Although many people’s first thought about carpenter bees is that they are a pest and should be removed, carpenter bees are a critical part of the ecosystem. Along with most bee species, they provide an essential benefit in pollination and are often threatened by humans and our activities.
- Although carpenter bees are a long-lived, large bee species, they have many natural predators, including birds (like woodpeckers), rats, and other insects (e.g., ants).
- Pollution is another huge threat to carpenter bees. Pollution has debilitating effects on most organisms, directly and indirectly. Pollution poisons water sources, results in climate change and alters the soil composition. These consequences often have negative impacts on the local fauna and flora.
- Although carpenter bees benefit from human dwellings and fence poles in locations for nest building, the development of natural areas depletes flowering plants, removing available food sources for carpenter bees.
- Wide-scale use of pesticides. Many agricultural operations use pesticides to control unwanted insects from eating crops. These pesticides are usually generalized and don’t target specific insects, which means that carpenter (and other) bees may also perish once coming into contact.
Since carpenter bees live close to human settlements, spray drift may also occur while farmers spray their crops.
Many people specifically target carpenter bees with pesticides to prevent them from establishing nests in wooden structures.
Although many people consider them pests, carpenter bees are essential to the ecosystem. Some benefits they provide include:
Carpenter bees are essential pollinators of indigenous and agricultural plants. These plants include:
Carpenter bees are also important pollinators of almonds and Brazilian nuts (Bertholletia excelsa).
Aside from commercial crops benefiting from carpenter bee pollination, these bees are critically important pollinators of indigenous plant species.
Due to a carpenter bee’s “buzz pollination,” flowers drop a huge amount of pollen. Carpenter bees collect this pollen for food, but it collects on their legs (especially the females and their brushy leg hairs), heads, and other body parts.
As they travel between flowers, they pollinate along the way, a critical component of natural vegetation persisting.
Related to pollination, carpenter bees are not specialized to use only one type of plant species or growth form. Instead, they forage from many different species. What is important about this is that insect populations (and particularly pollinators) fluctuate from year to year.
In years when a particular pollinator species are in decline, carpenter bees “fill the gap” left by that species and perpetuate the reproduction of the plants they would traditionally feed on.
Aside from their generalist nature, carpenter bees’ size and hardiness allow them to pollinate during inclement weather conditions that prevent other bee species from getting the job done (i.e., the cold and rain have a slightly reduced impact on carpenter bees).
Aside from pollinating natural and agricultural plants, carpenter bees are a vital part of the ecosystem’s food web. Many bird species, including woodpeckers, feed on carpenter bees. Although this may not seem too important, there is tremendous value in promoting a healthy food web.
There’s a great example to put it into perspective. If you’re sitting in an airplane and someone walks up, removes a bolt from the floor, then walks away. You’d panic, but not for too long as the plane is still flying. But then that person comes back, takes out another bolt, then walks away.
Eventually, there will come the point where the airplane falls apart from losing too many pieces.
The ecosystem is the airplane. If we keep removing certain species at liberty, there will come the point where the “plane” falls out of the sky.
If you had to choose a bee species to keep you company, you could do far worse than carpenter bees. Although males are showy and may dive-bomb unsuspecting intruders, for the most part, carpenter bees are not aggressive, and the chances of a female stinging you are very slim. You’ll need to go out of your way to disturb or handle them before they’re likely to sting you.
Although carpenter bees are necessary for healthy diversity, unfortunately, they cause some negative impacts. The drawbacks of carpenter bees include:
Carpenter bees’ nesting behavior causes damage to the wood around your home, including rafters, beams, fences, decking, and other critical parts of a building’s framework. Although most of the damage they cause is cosmetic (i.e., it detracts from the appearance of the building), if left for many seasons and if there are many carpenter bees at work, they can cause structural damage.
Aside from structural damage, carpenter bee nesting opens up wood for secondary infestation by carpenter ants, other insects, and fungi that attack wood.
With carpenter bees come predators. Woodpeckers break open wooden structures to get at these tasty treats, which causes much more damage to structures than carpenter bees do. Rats and mice are also an issue in chewing through wood/being attracted to your structures.
Although certain types of wood, like Cedar and Redwood, contain natural insect repellent properties (chemicals or they are too hard to chew into easily), carpenter bees don’t eat wood, so they use a wider variety of wood other insects usually avoid.
Aside from damaging wooden features around buildings, carpenter bees leave a yellow-brown stain around their nests. These fecal stains are difficult to remove and can become unsightly.
There are two approaches when you have a “carpenter bee problem.”
- Removal of the bees.
- Coexistence with the bees.
Although carpenter bees are a necessary part of the ecosystem, they cause unsightly holes in beams and other wooden structures, which could become structural issues over time.
Therefore many people choose to remove carpenter bees. However, preventing them from becoming an issue in the first place is a better option.
You prevent carpenter bees by using pressure-treated, stained wood. Unfortunately, this does not always help, but it is a step in the right direction. Painting your exposed wood is another useful management tool.
Using a harder type of wood will also discourage carpenter bees from boring into structures.
To prevent bees from returning to previous nesting sites, you can seal the old nests with steel, putty, wood sealer, caulk, or pesticides. You’ll need to close up these holes before the females begin laying their eggs.
Other methods of deterring bees from your structure include:
- Citrus oil deters carpenter bees, as the smell is off-putting.
- Almond oil is another natural deterrent that you can use to stain wooden surfaces.
- Wind chimes. The movement, noise, and vibrations of wind chimes will also help to deter carpenter bees who don’t appreciate these.
Replacing wood that carpenter bees made nests in is another option to reduce the likelihood of returning.
Sometimes prevention is not enough, and the nest needs to be removed. The best option, in this case, is to call a professional exterminator/pest control company. Although carpenter bees are not aggressive, disturbing their nest is a sure way to upset the females enough to make them sting you repeatedly.
Once the bees are removed, you’ll need to ensure they don’t return/and other bees don’t move in by replacing or repairing the wood.
The other option is to embrace carpenter bees as assets. We’re not suggesting letting them destroy your home, but by setting up a designated “carpenter bee nesting zone,” you could channel the bees to a particular area away from your home.
Many people do this by installing several untreated 4×4 softwood planks/poles for carpenter bees to use as nests near their gardens.
The great part of this strategy is you’ll provide important pollinator species with a home, reduce the likelihood of them damaging your home, and you’ll have a spectacular view of carpenter bee shenanigans during the spring and summer as they buzz from flower to flower, and the males defend their territories.
It’s important to note that, although you’re providing an alternative nesting site, some bees may try to bore into your important wooden structures. You’ll still need to ensure that you take preventative measures to reduce the likelihood of this.
Carpenter bees are distributed globally and are a critical part of ecosystems as pollinators and the food web. Most carpenter bees are in the warmer southern areas from west to east within the US. Carpenter bees are considered pests by many due to their nesting habits. They bore into wooden structures to make their nests, laying up to 10 eggs in individual compartments and sealing them off with a saliva and sawdust mixture. Preventing carpenter bees from invading exposed wood by painting or staining it and providing the bees with other wooden objects to use as a nest is the best way to manage them.