The eastern carpenter bee: an unloved nectar-robbing bee

Emblazoned t-shirts, coffee mugs, and license plate frames exhort us to “Save the Bees!” Scores of organizations single out species of concern, such as honey bees or native bees, while others promote any old bee. According to a representative of the Xerces Society, bee training seminars that once attracted a half-dozen participants now attract hundreds.

But regardless of all the attention, one species in North America is slipping through the cracks, failing to make the cut amidst all the bee love. Many people who are otherwise bee-centric are perfectly content to slaughter this one particular species. I’m not thinking about non-native woolcarders or the introduced Asian shaggy digger bees. No. I’m referring to our own native eastern carpenter bee, Xylocopa virginica.

The eastern carpenter bee is a pollination wunderkind. It is a large hulking species adept at sonication, that essential but rare trait that allows a bee to lock onto a plant and quiver, shake, and shimmy until the pollen explodes from its hidden chamber. Other sonicators live in the wild for sure, including bumble bees and some leafcutters. But with our love of the Solanum — such as tomatoes, potatoes, and eggplants — and the Vaccinium, including blueberries and cranberries, you can’t have too many sonicators.

So what about this charismatic bee crosses the line? Why does her photo grace the walls of the post office? The answer centers on territoriality. Not hers, but ours. We don’t like things living in — or remodeling — our homes uninvited. “Mine!” we declare. “My house, my barn, my lawn furniture.” So we mark her for destruction, no matter what she could have done for our environment and grocery shelves.

An abode of redwood

When I was a kid, my parents bought a circular redwood picnic table made of thick lumber, lovingly constructed, and quite expensive. Soon after delivery to our patio, a large carpenter bee showed up unannounced. She hovered at the edge of the table and drilled straight into the wood with a high-pitched whine reminiscent of a dental office.

After my mom shooed her away, I stuck my finger in the hole. It reminded me of a tiny test tube, rounded at the bottom and smooth as glass — the coolest thing ever. I was enchanted, but my mom was livid. She marched toward the house, promising to be right back.

Where humans go, carpenter bees follow

Like cats, carpenter bees prefer to live near humans who surround themselves with useful objects. Like us, carpenters admire fence posts, windowsills, fascia boards, railings, decks, shakes, and garden gates, and if the wood is unpainted, so much the better.

That carpenter bees actually practice carpentry on those items leads to trouble. They adore new wood, especially softwoods such as pine, fir, cedar, and redwood. They search for lumber thick enough and soft enough to excavate a nest in their own trademark fashion, but if no milled lumber is available, cordwood or a dead tree will do.

A carpenter bee’s tunnel

The build goes like this. The female drills straight into a piece of wood perpendicular to the grain. At about one body length — or roughly half an inch — she makes a hard ninety-degree turn. From there, she follows the grain, clearing a spacious cavity large enough to lay her eggs and accommodate the next generation. These hollow caverns are called galleries.

The female shoves most of the shavings and sawdust outside. Sometimes you can see it drifting in a cloud or discover a fresh pile on the ground beneath an excavation. They reserve the rest of the shavings for partitions that will separate individual egg chambers. Like many bees, the female begins a family at the far end of a tunnel by fashioning a nectar-laced pollen ball and laying an egg on top of it. Then she builds a particle-and-resin partition before beginning the next brood cell.

A carpenter bee egg is enormous, one of the world’s largest insect eggs. While a honey bee egg measures about 1.5 mm long, a carpenter bee egg reaches 15 mm. But its rarity tempers the egg’s size: an average female carpenter lays about a half-dozen in her entire life.

A maze of tunnels

One tunnel in a piece of wood is annoying, yet not too damaging. But carpenter bees possess a genetic trait known as philopatry, meaning subsequent generations nest close to home if they can. Some will even return to their natal nest. Soon-to-be moms are social enough to share a front door with other moms, each excavating a private nest from the shared vestibule.

After a few years, wood that once hosted a single tunnel becomes laced with compound galleries, often running parallel to each other along the grain. The multiple excavations can cause structural problems that may remain hidden. What appears as solid timber from the outside can be a house of cards — a catacomb beneath a thin veneer of wood, ready to collapse at any moment.

Other annoying habits

Drilling into homes and possessions is the major complaint against carpenter bees, but not the only one. Bees going in and out of their homes like to defecate at the nest entrance, leaving golden-brown streaks that stain the wood below. Apparently, even people who can overlook the hole are less philosophical about the fecal deposits, describing them as disturbing or low class. As anyone with honey bees knows, a quick squirt with the garden hose only makes the spots glisten.

In addition, some gardeners complain about the damage carpenters inflict on their flowers. Known for nectar robbing, they never hesitate to bite into the base of a corolla to access the nectar within. Although carpenters are excellent pollinators, they are big and unable to fit into skinny flowers with long tubular petals. When a svelte flower promises a good meal, the carpenters bite their way in, leaving slits in the petals that turn brown along the edges.

Because the slits are inviting, bees not adept at petal-biting will also visit the nectar cafe, enjoying a meal ready to eat. Honey bees, especially, like to take advantage of pre-split feed bags.

And finally, some homeowners complain that carpenter bees attract woodpeckers. The woodpeckers can detect brood under the thin veneer of wood that covers the galleries. With little effort, the birds can poke into the wood, casting splitters and carving holes.

The intimidating males

Known for intimidation, trespassing, and harassment, the males also have a PR problem, if not a mugshot in the post office. Because of their aggressive behavior, many folks shy away from them, fearing an attack. A sturdy bee hovering in midair while making prolonged eye contact can be offputting, but that is exactly what they do. Although they are all bluster and pomp, with no weapons beyond beady eyes, people give them a wide berth, preferring to exterminate rather than ignore them.

Like other male bees, male carpenters have no stinger, but they gather in agitated groups and make aggressive passes at all who enter their territory. They are unimpressed with your size or your ownership rights, so they try to make you leave.

How to identify a carpenter bee

The eastern carpenter covers a lot of territory in North America, ranging from southern Canada to Southern Florida, and from the Atlantic coast as far west as New Mexico. Because of their enormous size, they get confused with bumble bees. But eastern carpenter bees have a shiny, nearly hairless abdomen compared to the scary hairy abdomen of a bumble bee. In addition, the head of the female is extremely wide, like a buffalo. The male has a prominent yellow facial patch, nearly square, that distinguishes it from a bumble bee. The thorax and first abdominal segment (T1) in both sexes feature yellow hair.¹

Other species of carpenter bees live in the southern regions. The southern carpenter bee, Xylocopa micans, lives in southern Florida and along the gulf coast into Texas. We find other species in the American southwest and northern Mexico, including the valley carpenter (X. sonorina) and the western carpenter (X. californica). Some others have moved north from Mexico, including subspecies of the horsefly-like carpenter (X. tabaniformis).² Oddly, considering its abundance of softwoods, the Pacific Northwest is devoid of all Xylocopa, at least for now.

Worldwide, many species of carpenter bees are famous for having sexual dimorphism, meaning the males and females look nothing like each other. For example, the valley carpenter female is plain black while the male is a striking golden yellow.

An invasive enemy

In the early 1990s, a pest of the eastern carpenter bee quietly entered North America. The sculptured resin bee, Megachile sculpturalis, is a long dark bee in the leafcutter genus that nests within wooden holes and cavities. Discovering that native carpenter bee tunnels were much to their liking, the sculptured resin bees quickly spread to all states east of the Mississippi.

Superficially, the sculptured resin bee looks similar to the eastern carpenter. It is a large black bee with rust-colored hair on its thorax, and because it hangs around carpenter bee holes, it is frequently mistaken for one. But the sculptured resin bee is elongated with a narrow abdomen as wavy as the surface of a plastic water bottle. In addition, the female has large mandibles and carries pollen under her abdomen, not in a pollen basket.

The resin bees can be brutal to carpenters that build a desirable tunnel. The interlopers attack the carpenter and smear it with sticky plant resin until it can no longer fly. Observers have also witnessed resin bees biting the heads of carpenters and stinging. Once the maimed builder is out of the way, the resin bee moves in, leaving the carpenter to die.³

An easy fix for carpenter bees?

With all their assorted debits, it’s easy to see why carpenter bees wear a bullseye on their backs, marked for extermination. But how aggressive should we be? Is there a way to save these top-of-the-line pollinators and our personal structures?

When my mom came back to the patio after discovering the carpenter bee damage to her picnic table, she carried a circular vinyl tablecloth. With zero entomological training, she adjusted the cloth to hang about six inches over the perimeter of the table. It disappointed me no end because the bee was cute, but I could see her point. The cloth worked, the carpenter never returned, and no one had to die.

To control carpenter bees, you can either deter them or kill them. Some folks like to spray repellants such as citrus oil or almond oil around the entrances to repel returning bees. Once the bees are out, the holes can be plugged with wood putty, plastic wood, or a wad of steel wool. Other people like to use loud music, wind chimes, or diatomaceous earth, none of which I can vouch for.

I know entomologists who simply snag them with a butterfly net and then pinch each one. Although lethal, this method is quick, doesn’t accidentally kill other species, doesn’t poison your environment, and won’t annoy the neighbors.

Recall that carpenter bees are philopatric, preferring to nest near their birthplace. That means that once you rid your immediate area of carpenters, others are unlikely to arrive. After you net the adults in spring, you should be carpenter-free for the rest of the year.

Holding carpenter bees at bay

Lots of people recommend paint and varnish for all wooden surfaces where carpenters are a problem. Although carpenters prefer uncoated wood, if they can’t find it, they are likely to use your neatly painted windowsill. One workaround is to give them an alternative, such as a pile of untreated, unpainted softwoods at a comfortable distance from your house.

Of course, whenever money can be made, someone will devise a product for your predicament. Right now, carpenter bee traps are a thing, available everywhere.

The traps come in various types, some with poison, some with pheromones, and some with neither. Basically, a bee enters an attractive-looking hole lured by pheromones or simply by looks. Once she enters, she either encounters insecticide or drops into a catchment container from which she cannot escape.

Personally, I like to avoid insecticides. The ones in common use are lethal to all bees, not just carpenters. Although there is not much chance of collateral damage, I prefer to avoid the entire pesticide issue.

However, the traps that don’t use insecticides allow the bees to die slowly. Some people have said that even after several days, some bees were slowly writhing within the catchment jar, which seems unnecessarily cruel. Others have mentioned seeing some amount of by-catch in the jars, especially bumble bees.

Bee condos won’t work for carpenter bees

Oddly enough, a fairly common “solution” sold by many pest control companies and garden centers is a mason bee condo. Advertisers claim the tubes lure carpenter bees away from your house and yard by giving them a place to live. That is nonsense.

Recall that carpenter bees have a signature ninety-degree bend in their tunnels that occurs at about one body length from the entrance. Because there is nowhere to turn within a bamboo tube, they are not attractive to carpenters at all. Entomologists recommend that wood designed to attract carpenters should be softwood, at least two inches by two inches in cross-section, and the length should run with the grain. This allows the carpenter to drill perpendicular to the grain and then make her right-angle turn.

Weighing the options

I have no simple answers, but I urge you to think about these bees before dividing your pollinators into good ones and bad ones. Yes, carpenters can be a nuisance, and yes, you don’t have time for them, but think anyway.

If you must kill them, I urge you to net and pinch for a week to see if you can reduce their numbers without resorting to cruelty or poisons that can affect other insects. If nothing else, remember that saving pollinators begins at home.

Rusty Burlew
Honey Bee Suite

Acknowledgment

Many thanks to nature photographer Bob Noble for his gorgeous photographs, all taken in the Heart Lake Conservation Area of Brampton, Ontario.

References

1 Danforth BN, Minckley RL, Neff JL. 2019. The Solitary Bees: Biology, Evolution, Conservation. P. 365. Princeton: Princeton University Press.

2 Carril OM and Wilson JS. 2021. Common Bees of Eastern North America p.163–164 Princeton: Princeton University Press.

3 Frankie GW, Thorp RW, Coville RE, and Ertter B. 2014  California Bees & Blooms: A Guide for Gardeners and Naturalists p. 70-76. Berkeley, CA: Heyday Press.