Borer Bees III: Carpenter Bee as Native Pollinator

This is a deeper dive into carpenter bee ecology, supplemented by first-hand observations and my own speculations. We look at native flowering cycles in the Virginia Blue Ridge Mountains, remember the American chestnut, and consider the resources for climate change offered by such a widely adaptable generalist pollinator as the carpenter bee. More deeply, we acknowledge the transformative power in relating with a bee-ing for its own sake.
Photo by Katy Morikawa

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As I’ve conducted my experiments in carpenter bee housing, recounted in “Consider the Borer Bee”, Episode 24 and “Borer Bees II: The Bee House Saga, Episode 26, I’ve become very curious about the flowers they feed on and the role they play in the environment. As native pollinators, surely their bread and butter would be native flowers, flowering in succession across the growing season. (See Consider the Borer Bee for more details on their life cycle and why I would think that). At our house, we’ve never grown ornamental flowers– too many deer and neighboring goats for that! We also don’t have many wildflowers, but mostly trees and grasses.

Trees in Flower

As I looked around at the landscape this May while the carpenter bees busily built their brood chambers, I saw masses of white flowers throughout the tree canopy: the locust and wild cherry trees were blooming, seemingly in perfect time with the carpenter bees’ active mating and nesting season. As the weeks passed and the locust and wild cherry blooms faded to gold and then brown and then fell, I saw that the younger wild cherries, lower in the forest at large bush height still were following with their own later succession of blooms, surrounded by blooming tulip poplar, wild roses, and blackberry. Interestingly, of these, only the wild roses aren’t native and I have not seen any carpenter bees on them despite their heavenly fragrance! (I love the multiflora rose and cannot demonize it no matter what the naturalists say!) In fact, the only carpenter bee I did see feeding was climbing around in a locust flower cluster. So, that hypothesis was confirmed at least as to a food source.

Locust Trees and Carpenter Bees

I got really excited when I realized that both locust trees and wild cherry trees tend to have a lot of dead limbs. You see the broken and dead branches all over the forest here in the Blue Ridge Mountains of Southwest Virginia, along with standing dead locust trees. Suddenly, it seemed like more than a coincidence. Might borer bees burrow into old dead locust limbs or trees? Then when they emerged in spring, pressed with provisioning their brood chambers, the locust (and the wild cherry) would be in bloom all over the forest. The bees would have enough flowers and nectar for provisioning egg chambers, and would pollinate the trees in the process. Carpenter bees are known as generalist pollinators, and everything I’ve seen indicates their adaptability to local conditions. But the critical spring breeding season must be anchored to a reliable native source of flowers blooming at the right time! I haven’t seen carpenter bee brood chambers in old dead locusts yet (they’re hard to get to because they’re usually really high up, and my eyesight is not what it used to be). Also haven’t seen them feeding on wild cherry blossoms. But I did spot woodpecker galleries in an old mostly-stump locust tree by the Little River which was still sending up flowering branches from low at its base, and growing amidst a stand of locust trees in full flower. This is where I saw the carpenter bee feeding on a locust flower cluster (which is the featured image for this post). Where there are woodpeckers there may be borer bee brood chambers!

The Beauty of Dead Trees

I find myself looking at standing dead trees in a whole new light, struck by their elegance and even their beauty. This is new for me. For years, I thought of locust and wild cherry trees both as trash trees largely because of that tendency. True, of late, I’ve been trying to appreciate them and I actually do now genuinely love locust trees. They’re antennae! I believe they move energy up and down the ethers (but that’s a side tangent).

I know I’m not the only one who has disliked the look of untidy dead and broken trees. I used to compulsively imagine pruning and cleaning them up, even when I saw them in the National Forest! I’m sure that many people living in this kind of woodland do regularly maintenance their woods, clearing out old dead wood and pulling down snags. Certainly this kind of dead wood wouldn’t be allowed to stand in suburban neighborhoods. How much, I wonder, has human tidying behavior reduced carpenter bee habitat, thus applying pressure to human dwellings and strucures?

Flowering black locust trees in our back yard, complete with broken limbs and dead trees.

Woodland Pollinator?

It’s said that carpenter bees prefer to nest in pine, cedar, and cypress trees. But we don’t have many of those here in Floyd County in the Virginia Blue Ridge Mountains and we have plenty of borer bees. Furthermore, although they can travel up to 7 miles, per one source I found, they can’t travel forever. So, given that they nest in wood while eating only flower pollen and nectar, surely they co-evolved with flowering woodlands? To my knowledge, conifer trees don’t provide any food source for carpenter bees. This means that where they do nest in those trees in the wild, they’d need to be surrounded by flower food across the spring, summer and fall months.

The carpenter bee we have around here, Xylocopa virginica, has a really vast native range. Also, btw, an entomologist made the statement on this podcast that they are always native wherever they’re found (wow!). From the Atlantic Ocean to Rocky Mountains, and from the Great Lakes to the Southern Gulf Coast, the Eastern carpenter bee is adapted to a wide variety of bioregions. I am struck all the more by their adaptability when I remember that they survived the total collapse of the Appalachian Woodlands with the virtual extinction of the American Chestnut tree.

Elegy to the American Chestnut

It’s easy to forget that our native forests here in Appalachia were radically different a hundred years ago when the American Chestnut dominated the landscape. Descriptions of that landscape are heady and merit a long quote from Our State: Celebrating North Carolina:

Once, the springtime canopies of western North Carolina forests were an unmatched floral display […] The American chestnut rose 100, sometimes 120, feet above the loamy forest floor. Most were nearly barren of branches for 50 feet or better […] “the redwood of the East.” […] massive trunks, […] they lorded over the forest. In most places, every fourth tree was a chestnut, and along vast ridges, fully 7 out of 10 trees would have been of the tribe Castanea dentata […] and they put on a pageant.

A starburst of pearly white catkins tipped nearly every branch of the massive trees. Each catkin was nearly half a foot long, streaking like a comet’s tail against the dark surrounding foliage. In the spring, you could stand atop ridges and watch the white flowers roll like surf for miles. In the fall, you could gather the fruits of these flowers, the sweet, starchy chestnuts clad in prickly burs, by the barrelful.

“The Lord of the Forest: the American Chestnut,” Our State [2]
Loggers in a Great Smoky Mountains forest, mid- to late 19th century.

Now, the American chestnut is virtually extinct, and the forest landscape that dominated the Blue Ridge Mountains for millennia is changed forever. This majestic tree was a true provider of food for so many species, including nectar-feeding bees. As an old-timer, Noel Moore of Rabun County, Georgia, recalled in 1980, “We’ve never had a honey crop like we did since the chestnuts died, because there’s not that much nectar in the wild now. Whenever chestnuts bloomed, in the morning, early, the trees looked like just the whole tops were alive with honeybees working on getting the nectar.”[3] We don’t know for certain whether carpenter bees feasted there, but it seems likely. Especially considering that honeybees are not native to the New World and did not co-evolve with the American chestnut. Co-evolution is the name of the game with native species, and we know that the tree produced high quality nectar in profusion.

The article featuring the above quote mourns the loss of our opportunities to understand the many complex lifecycles built around this tree, although it makes perfect sense to me. I can just see the carpenter bee feasting on chestnut flowers which bloomed in June shortly after the locust blooms faded. Black locust (Robinia pseudoacacia) is also native to this part of the world, despite having been transplanted all over the world and acting as an invasive species in many places even on this continent. Here in Appalachia, we are in its native range,[4] which means it coexisted within those massive American chestnut forests. And in fact, the overlap between the maps of their native ranges is striking and interesting.

Native Range for American Chestnut

Native range of the American chestnut tree (Castanea dentata). From American Chestnut Foundation.[5]

Native Range for Black Locust

Natural distribution map for Robinia pseudoacacia, black locust. By Elbert L. Little, Jr., Public domain, via Wikimedia Commons.

I don’t remember seeing evidence of carpenter bee brood chambers in chestnut wood. But they would have drilled into dead branches or other wood unlikely to be turned into lumber. Chestnut boards comprise the vast majority of chestnut wood I’ve seen. I’ll have to look again at the old fence posts on our property in North Carolina to see what I can see. But even if they didn’t nest in chestnut trees, they surely ate of their bounty.

What Now?

In the wake of the devastating loss of the American chestnut, many species went extinct, but the Eastern carpenter bee has survived. As a generalist pollinator, already adapted to a wide range of bioregions, it adapted to this massive setback. I’ve seen it feeding on exotic ornamental flowers in suburban gardens, flowers that are not from this part of the world at all. And as we all know, it has come to seek out human wood structures for nesting. I have to wonder how much of this preference reflects the loss of a major food source (and presumably habitat) that this bioregion used to provide? Is it possible that the Eastern carpenter bee has reverted to boring into human structures not just because of a loss of habitat but also to conserve energy? Conserving energy during brood chamber construction would leave the bees with more energy for foraging for food now that the wild has lost so much of its nectar, as the old-timer, Noel Moore, observed. It’s enough to make you mourn, Gone is the sweetness in the world!

If Xylocopa virginica lost a major food source in this bioregion, the American chestnut, the redwood of the East, should we be concerned about protecting it as it adapts to new conditions by moving into our home siding and feasting on our exotic flower gardens? After all, it’s a new world, right? Perhaps it is no longer needed as much as it once was and we should let nature take its course. People can exterminate the bees and we can move on into the new world we live in.

But I think that as well as remembering “the least of these,” and that we should not assume that something is no longer needed, or is unimportant, is worth remembering. But also, I find another argument in the carpenter bee’s marvelous ingenuity. The carpenter bee is an adaptable and effective pollinator. It is still perfectly designed or co-evolved to pollinate many plants in North America. Furthermore, I believe flexibility is a characteristic of carpenter bees worldwide (not 100% sure on that, but it is true of Xylocopa virginica). Right now, during the Sixth Mass Extinction, we are facing unprecedented climate change. We will need nimble, adaptive pollinators able to face the changes with us. Maybe the carpenter bee is just what we need for these changing times. Maybe the journey to cooperate with it is just the journey we need. Because maybe the greatest gift lies in connecting, communicating, and delighting in a bee-ing for its own sake. (They are very individualistic). The wonder of discovering a collaborative relationship across species, and where we least expected it, offers a truly nourishing kind of magic without which we might not survive the century.

Strange Parting Fact

The American black locust tree has been exported to mid-western Europe and grows widely from Italy to Hungary. It is the source for the monofloral honey marketed as “acacia honey,” prized as a delicacy for its sweet, light-colored, delicate floral flavor, and resisitance to crystallization due to its high sugar content.[6]

U. S. apiaries like The Savannah Bee Company are promoting acacia honey as both a native honey and a European delicacy.

Local U. S. apiaries like The Savannah Bee Company are promoting acacia honey as both a native honey and a European delicacy. Based on this honey’s rave reviews, it’s hard to believe we in the U.S. are only now discovering its virtues. For my whole life, the prized tree for honey has been the sourwood, also native to this region. Before that, it was apparently the American chestnut. In any case, this does speak to and confirms the high-quality of black locust as nectar source for native bees.

My carpenter bee house looks out at my favorite locust tree in the whole world. I call it The Sentinel, and it lines up almost exactly with the equinox sunrise position.

Update

The statement about the total dominance of the American chestnut over the entire Eastern forest is exaggerated, but seems to have applied mostly to the lush mountains of the Smoky Mountains National Forest and similar bioregions. The American chestnut was common in many areas but needed a lot of water and thrived in the mountains of Appalachia in places that stayed moist, but not in the drier regions.

The Full Bee Series

Episdoe 24, Consider the Borer Bee

References

  1. American chestnut. In Wikipedia, The Free Encyclopedia. Retrieved 18:42, May 30, 2022, from https://en.wikipedia.org/w/index.php?title=American_chestnut&oldid=1088371741
  2. The Lord of the Forest: the American Chestnut. Retrieved May 30, 2022 from Our State https://www.ourstate.com/american-chestnut/
  3. Moissett, B. (March 4, 2013). Pollinators of the American Chestnut. Retrieved May 30, 2022 from Pollinators http://pollinators.blogspot.com/2013/03/pollinators-of-american-chestnut.html.
  4. Robinia pseudoacacia. In Wikipedia, The Free Encyclopedia. Retrieved 02:42, May 30, 2022, from https://en.wikipedia.org/w/index.php?title=Robinia_pseudoacacia&oldid=1089479918
  5. Natural Range of the American Chestnut Tree. Retrieved May 30, 2022 from The American Chestnut Foundation https://acf.org/the-american-chestnut/native-range-map/.
  6. Monofloral honey. In Wikipedia, The Free Encyclopedia. Retrieved 02:42, May 30, 2022, from https://en.wikipedia.org/w/index.php?title=Monofloral_honey&oldid=1062933894

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