I am drunk … drunk with the smell of locust blossoms. The long, dull winter is finally over, the grass is finally green, and the irises and black locust trees (Robinia pseudoacacia) are blooming. I want to do nothing but feast my eyes on the colorful irises and breathe in the sweet smell of the locust flowers all day long. The bumblebees gathering nectar from the blossoms cannot stay away either. Of course, their efforts ensure food for the young bees that are developing in underground nests, while my lack of effort ensures that my “to-do” list will be even longer tomorrow. But still I am pinned to this place in space and time, surrounded by black locust trees dangling their white, honey-scented clusters of flowers.
BLACK LOCUST FLOWERS produce a lot of nectar. A local beekeeper keeps a couple of hives of honeybees on my farm to take advantage of this bounty. In exchange for hive space he occasionally gifts me with a quart of his honey. So I, too, get to fuel my body on the nectar from the locust blossoms. The locusts are so generous with their nectar that they even provide some outside the flowers—in little ducts near the leaves— for insects such as ants and ladybugs. Evolutionary biologists believe that these “extrafloral nectaries” must have evolved because plants with the extra ducts attracted beneficial insects that enhanced the plants’ survival and allowed them to produce more offspring.1
Why would having resident ants be an advantage for a tree? One reason might be that they are good protectors. All plants are plagued by insects that want to eat them. But plants cannot move away from insect swarms or clean themselves like animals can. Instead the plants must depend on their own leaf chemistry and on the services of the beneficial insects they are able to attract. Ants help keep the trees clean by attacking and eating any insect eggs and larvae they find. This cleaning service reduces the number of insects eating the leaves.
A few kinds of insects, though, are safe from the ants’ attacks; in fact, the ants protect them, guarding them and milking them like a herd of miniature cows. Tiny sucking insects like aphids and treehoppers get their nourishment by sticking their needlelike mouthparts into plant vessels carrying the sweet sap. They remove nitrogen and some of the sugars from the sap for their own use, but the rest of the water and sugars in the sap move through the insect’s body and come out the other end as a sticky substance called honeydew, a polite name for aphid urine. If you have ever parked your car under a leafy tree on a warm summer day, you might have returned to find it sprinkled with “sap.” That “sap” is not from the tree directly but is the liquid that has passed through the bodies of sucking insects.
Ants protect the aphids for their own benefit rather than attacking them for the benefit of the tree. When an ant strokes an aphid with its antennae, the “milking” action stimulates the release of honeydew. Ants drink the honey-dew, a good source of water and nutrients, directly from the surface of the insect “cows.” If it is a year of few aphids, however, the ants will not starve if they are on a plant that provides nectar through extrafloral nectaries.
In large numbers aphids are harmful to trees because they remove sugars the trees have produced to meet their own energy needs. Other beneficial insects, such as ladybugs, eat aphid eggs and larvae and help to keep their numbers in check. The ladybugs will also drink from the extrafloral nectaries, which may keep the ladybugs loyal to a tree in the absence of aphids. When sucking insects do appear, the beetles are present to feed on them.
WHEN TAKING A BOAT up the river or a car up the road, I see locust trees here and there. Certainly the locust is not a dominant tree in any of the area’s forests, but they always look “at home.” The locust trees seem such a natural part of the landscape here that for a long time I assumed that they were native to the area; when I checked a range map, though, I learned that they were not originally found on the East Coast at all; they are native only to the Appalachian Mountains.
No one knows why the first black locust trees were planted in this area, but I like to think that they were planted as a source of fence posts. Black locust wood, once dry, is very hard and slow to rot. In the days before treated wood, rotting fence posts were a problem for farmers who were trying to contain their animals. Building a fence took a lot of effort, and the farmer wanted it to last for as long as possible, so black locust wood was a good choice.
MY FRIEND doesn’t like it if you call her property a farm. She calls it an organic, biodynamic garden. She plants according to the phases of the moon, and she has an ark-load of animals that need to be kept away from the many fruits and vegetables she grows. My friend refuses to use treated wood for her fence posts because it is toxic and the toxins can leach into the ground—and from the ground into the plants, and from the plants into the animals.
How many fence posts around our neighborhoods are leaching poisons into the ground? And how many docks are leaching poisons into our waterways? The manufacturers of the treated wood products will tell you that the amount of toxin that leaches out is minuscule and unlikely to harm anything. But those of us who pay attention to such things know that we are being asked to make a thousand such compromises every day— until ultimately we have compromised away the health of the earth. And the health of our bodies is not a thing apart from the health of the earth. So in her garden my friend makes no compromises; she will place a special order for black locust posts.
Others around the world must have found the black locust useful as well. It was the first tree species introduced to Europe from North America. The gardeners of King Louis XIII of France planted the locust trees for their beauty, but now they are planted across the globe for a multitude of uses, including site restoration and wood production. Black locust trees are in the pea family, so instead of depleting soil nutrients where they grow, they actually improve the soil.
BLACK LOCUSTS are genetically diverse. This genetic diversity shows up in many ways, including the growth form of the tree (some varieties grow taller and straighter than others) and in the presence or absence of thorns. This week I looked closely at my trees to see if they were the variety with thorns or without. They did have thorns, and I was surprised when one of the “thorns” moved to the other side of the branch when it saw me looking at it. When I leaned over to look at the other side of the branch, the thorn again moved around to the side away from me. My entomologist friend calls this “playing squirrel.” I found it fascinating that the little thorn-imitating insect knew when I was looking at it. We played together for a while before I left it alone. The insect was a locust treehopper (Thelia bimaculata), a species found only on black locust trees.
I wonder if the black locusts spreading around the globe have spread the treehoppers as well? The little hitchhikers are certainly common, but as far as I know no one has ever checked all the populations of black locust to see if they all have treehoppers. Although the idea of traveling the world to find out is tempting, the same information could be obtained easily through the Internet by asking botanists to check the trees in their area and report the data to a central location.
The female locust treehopper lays her eggs at the roots of the tree, just beneath the leaf litter. When the little nymphs hatch from the eggs, they climb up the locust trunk and find a place to insert their sap-sucking mouthparts. Ants (primarily Formica obscuripes) protect and milk these tree-hopper nymphs. By the time the nymphs mature into adults they have developed their characteristic thorn shape, which most likely evolved because it serves as a camouflage to protect them from whatever eats treehoppers.
THERE IS ANOTHER INSECT that is also dependent on black locust trees, but you are not likely to see it on the tree. The locust long-horned wood-borer (Megacyllene robiniae), or locust borer for short, is more commonly seen on goldenrod flowers. To complete its life cycle the locust borer needs both goldenrod (a yellow fall-blooming perennial) and locust trees. Luckily my farm has both. Check the goldenrod flowers for beetles that are slightly larger than fireflies (lightning bugs). The beetles will be black with horizontal yellow stripes, with one of the stripes looking just like the letter W. This bright pattern may have evolved to mimic stinging insects such as wasps and bees, which announce their ability to harm with striking black and yellow colors. This warning coloration may save the bees from being attacked once a predator recognizes its meaning. The mimics benefit from the deception because predators are likely to avoid them, too.
Once you have located the locust borers on a blooming goldenrod you are likely to notice that a number of them are mating. The goldenrod is a kind of singles’ bar for borers looking for mates. Regardless of species, it’s useful for organisms with sex on their minds to have a place where they can gather—it saves time and energy. But in addition to being a mating hotspot the goldenrod flower is also a source of food for the beetles. Their favorite meal is goldenrod pollen.
Once the pairs have mated and eaten, the females go off to lay their eggs. The female flies to a locust tree (I wonder if she uses sight or smell to find it?) and lays her eggs in little crevices in the bark. The eggs hatch in about two weeks, and the tiny larvae immediately begin chewing their way into the wood. When winter sets in they “hibernate” inside the tree, and when the warm weather returns they continue chewing their tunnels. By fall a borer larva is ready to pupate into the adult form, exit through the same hole it entered, and fly off to find a goldenrod flower and a mate.
The tunnels themselves do not do much damage to a tree, but they do create openings for fungal spores to enter. Is it chance or design that brings a spore from the fungus Phillinus rimosus into one of these passageways? Once again, we do not know the why or the how, but we do know that the fungus spores enter the holes made by the borers and that the fungus itself begins feeding on the wood. The wood, especially in the roots, begins to rot. The durability of the cut locust wood is no indication of the durability of a live tree. Black locusts are not long-lived trees; it is rare to find one over a hundred years old. Their life span roughly matches our own.
I have never witnessed a human dying; I have, however, witnessed a black locust dying. The tree was large and apparently healthy, perhaps fifty years old. Hurricane Gloria brought days of rain that softened the ground, and then a few hours of very strong winds. Through the window I could see that the locust tree was not recovering between gusts of wind; instead it was slowly beginning to lean. I could see the ground swell up near the base of the tree when hard gusts of wind pressed against the canopy. It was a much slower process than I had ever imagined, having seen many “tipped over” trees in the forest and having tried to re-create the event in my mind’s eye. The trunk soo veerryy slowly leaned further and further over, and the ground rose higher and higher, until at last the roots ripped out of the sod and the trunk came to its horizontal rest. I instinctively released the air I had been holding in my chest. Oooa. “[E]ven trees do not die without a groan” (Thoreau again).2
Now that I know about locust borers I wonder if my tree’s demise was related to their activities. Perhaps they opened the door for a fungus that grew in the roots, weakened the tree, and contributed to its fall. Could a microscopic spore, assisted by a little insect, have caused the demise of a mighty tree? Did Goliath meet his David? Some ecologists, who consider the black locust to be an invasive species, have suggested planting more goldenrod to benefit the borers, thereby assisting in the spread of the fungus and hastening the demise of the locusts.
But was my tree really dead? Black locust trees can produce sprouts from their roots. I had never noticed any sprouts coming up from the roots when the tree was standing. Once the tree fell, however, some roots remained in the ground, torn away from the trunk. The roots that remained buried in the ground somehow knew that this was the time to sprout top growth. A wondrous metamorphosis occurred in the cells of the root tissue, and buds formed that began to grow upward out of the soil toward the sky. The next year, in place of one large locust tree I had about fifty little ones. These new little trees had the exact same DNA as the one that fell; they were clones. So was my tree dead or not?
I was happy to have a replacement for my fallen tree, but I certainly didn’t need fifty. I chose three small sprouts that were spaced just right for a hammock grove and let them be; the rest I pruned to the ground. The roots continued to send up shoots, but I reasoned that if I kept cutting the shoots the roots would eventually run out of energy and die— saving me the trouble of digging them up.
It hasn’t quite worked out that way. Sometimes Mother Nature has a different idea, and it is usually best to at least listen to what she has to say. One of the many root sprouts came up in my iris garden. I didn’t want a locust tree in my flowerbed, so I cut it to the ground. A few weeks later, as I was weeding the bed, I noticed that the sprout was growing again, more vigorously than before. I tried to pull it out of the ground, but even when I used all my strength it would not budge, so I clipped it down to the ground again. It recovered, and again I cut it down. This went on for about two years until, as I was preparing to cut it once more, I had the sudden realization that this strong little sprout really wanted to live. So I would let it. It didn’t matter if I wanted a tree in my iris garden or not. Mother Nature had decided in favor of it, and she knows best. Now, instead of fighting the tree I just sit back and watch it. It is amazing how fast that tree grew once I finally left it alone. Today it is about fifty feet tall and a lovely addition to the garden. In fact, it is the very tree that has me pinned in place today, the one that sweetens the air I breathe, the one that feeds the bees. The irises still bloom at its base.
I feel proud and protective of that tree—perhaps something akin to how a woman who had considered abortion might feel after her infant had grown into a strong young adult. The life is no longer in danger … but the recognition that it once hung by a tenuous thread makes it that much more precious. As Rilke writes:
Namelessly, I have chosen you from afar,
You have always been right and now your sacred idea
is the intimacy of death. (75–77)
I have watched the saplings in my black locust grove mature, and this year they are finally strong enough to hold an adult in a hammock. It’s good to have dreams, but sometimes it’s good to let dreams have you, too.