What would our lives be like if we took earthworms seriously, took the ground under our feet rather than the skies high above our heads, as the place to look, as well, eventually, as the place to be? It is as though we have been pointed in the wrong direction.
—ADAM PHILLIPS, Darwin’s Worms, 1999
“ARCHAEOLOGISTS ARE PROBABLY not aware how much they owe to worms for the preservation of many ancient objects. Coins, gold ornaments, stone implements, &c., if dropped on the surface of the ground, will infallibly be buried by the castings of worms in a few years, and will thus be safely preserved, until the land at some future time is turned up.”
Darwin made this proclamation in the beginning of the fourth chapter of The Formation of Vegetable Mould, entitled “The Part Which Worms Have Played in the Burial of Ancient Buildings.” He went on to describe the excursions he or his son William took to excavation sites around England, including a farm in Surrey where Roman ruins were found, an abbey in Hampshire destroyed by Henry VIII, and the ruins of a Roman villa in Gloucestershire. He reported that worms had burrowed into the old stone walls, undermined foundations, and generally deposited a layer of castings that permitted grass and other plants to grow. After examining the sites of several ancient ruins, he concluded that the actions of earthworms “would ultimately conceal the whole beneath fine earth.”
In some ways, Darwin thought of worms as historians, covering the remains of one civilization and preparing the earth for the next. But earthworms can hardly be considered sneaky in their concealment; in fact, anyone who has ever watched a worm knows that it goes about its work in the most matter-of-fact manner. It is only carrying out the natural order of things, folding the ruins of a city, a farm, or a society into the lower strata of the earth. When our civilizations end, and when we as individuals die, we don’t ascend, not physically—we descend. And the earth rises up to meet us.
I read about Darwin’s visit to Stonehenge, where he saw firsthand that earthworms were drawing those ancient rocks down to their underground world, and I shared in his sense of wonder over the continual job of burial that they performed. Earthworms toil incessantly to carry us down to the depths of the earth with them, and ultimately, our efforts to resist are futile. Darwin must have taken some comfort in this; he never feared death, and he appreciated the natural order that this arrangement with earthworms suggested. In a way, looking down at those buried Roman ruins must have been like getting a glimpse of a kind of afterlife.
But even Darwin knew little about the civilization that existed down in the earth. The clumsy artifacts he uncovered would have held little interest to him if he had instead been given one glimpse into a microscope powerful enough to illuminate all the invisible creatures that inhabit the soil alongside earthworms. A new world would have been laid bare to him. Like a shipwreck diver distracted from his task by the aquatic world around him, Darwin would have soon forgotten about his ancient ruins.
Eternity can be found in the minuscule, in the place where earthworms, along with billions of unseen soil-dwelling microorganisms, engage in a complex and little-understood dance with the tangle of plant roots that make up their gardens, their cities.
A BACKYARD GARDEN is a miniature ecosystem, one that requires constant tinkering. Gardeners are always assessing whether their plots of land could use more alfalfa meal, less water, another layer of manure or mulch. Even the insect population can be modified, managed. Ladybugs can be purchased, lacewing eggs hatched, honeybees lured in, all in the name of keeping the garden in balance. Now even microscopic creatures can be ordered by mail and introduced to combat some pest, seen or unseen, wreaking havoc in the flower beds. It wasn’t until I met up with some of those mail-order microscopics that I began to get a glimpse of the vast unseen world in which earthworms are such a vital force.
When I moved to Eureka last year, I knew things would be different in the garden. The temperature here is always five or ten degrees cooler than it is in Santa Cruz. Fog hangs over Humboldt Bay most of the year, making a full day of sunshine a rare event, one that most homeowners celebrate by getting out to scrape the moss off the north side of the house. The seasons change slowly. Some would say that the only real difference between summer and winter—apart from a few blessed degrees of warmth—is that it stops raining in the summer.
This gave me plenty to think about when I first planned my new garden. The sage plants I relied on for year-round bloom would have trouble getting established here. Heat-loving vegetables like tomatoes and peppers would surely struggle in the cool, damp summer, although I would plant some anyway in the faint hope that my backyard would be warm enough for them. The angel’s trumpet, with its enormous, bell-shaped flowers, would certainly succumb to frost damage in winter. Only the lilac, which prefers a chilly winter, would do well here. I’d have to learn to appreciate the plants that would grow in this climate: rhododendron and azalea in the flower garden, cabbages and potatoes in the vegetable garden. In the middle of winter, when the moving van arrived packed full of plants from my Santa Cruz garden, I did what I could. I put them in the ground where I thought they’d do best, but it would be a year or more before they got established and the garden began to have a structure. I spent that first year nurturing tiny transplants along, heaping compost around their roots and pulling weeds. Soon the garden and I were in our second spring together, and it was showing me what it could do. The lavender hedge was filling in, and the daisies and coreopsis showed signs of a long blooming season ahead.
One thing I wasn’t prepared for was the insect population. I saw snails and slugs everywhere—on the buds of my daffodils, chewing young green pea shoots. There were aphids, but I was also pleased to find an abundant population of ladybugs, and they would keep the aphids in check. The real trouble involved the new pests in this garden, pests I’d never done battle with before. Furry black caterpillars massed on the underside of my artichoke leaves, eating holes until the leaves looked like fine lace. Tiny green caterpillars were making a meal out of my cabbages. Worst of all, some unseen enemy was sawing off seedlings as they emerged from the soil.
The first two pests were easy enough to control. The black caterpillars—tent caterpillars, I learned they were called—could either be picked off and dumped into a pail of soapy water or sprayed with an organic treatment that causes them to stop eating and slowly starve to death. The cabbage loopers, moth caterpillars that feed on cole crops, could be kept in check with the same spray, or I could encourage their natural predator, a parasitic wasp, to set up camp. Since parasitic wasps happen to like many of the same flowers I do—yarrow, tansy, alyssum—this was an easy concession to make. That left one more to conquer: the one cutting down my seedlings from the root.
I’d been paying a lot more attention to the soil now that I was keeping tabs on my earthworm population. I had a general idea of the kind of creature I was looking for—a grublike caterpillar called a cutworm that lived near the surface of the soil. I watched for it any time I was out digging in the dirt. Sure enough, before long I spotted one. It matched the description in my pest control book: “a fat, greasy, grey or dull brown caterpillar with a shiny head; found in the soil.” This one was curled in a tight circle just a few inches below the surface. Over time I would find that cutworms usually stay in that position during the day and venture out after dark to do their damage.
I flipped the grub onto my shovel and flung it into the street. This is how I usually handle snails, too: I toss them into the road and let cars drive over them so I don’t have to squash them myself. But it’s one thing to walk around the garden pulling snails off leaves and tossing them into the road; it’s another thing entirely to dig around in the dirt for cutworms. I could dig up half the garden looking for them.
It turns out that the best control for cutworms is a particular type of parasitic nematode, a microscopic creature that lives in the soil. It enters a cutworm’s body, releases bacteria that kills it, then feeds off the dead cutworm and lays eggs. I’d never added nematodes to my own soil, but I knew that garden supply companies sold them for any number of pest infestations: one worked against fleas in lawns, another worked against mole crickets, one attacked cutworms and squash vine borers, and one even attacked other nematodes like the destructive root-knot nematode that often plagued carrots.
I chose the nematode that was most effective against cutworms. I started small, ordering just five million. They arrived inside a slim sponge not much larger than a credit card. The sponge was sealed inside a plastic bag. A yellowish liquid oozed out of it. These, I took it, were the nematodes, immersed in some kind of solution. The whole package was smaller than a letter-sized envelope. All I had to do was drop the sponge in a bucket of water, wring it out, and spray the water around my garden.
How could five million creatures be alive in that sponge? How could something so small kill a cutworm, an inch-long grub? How would they even find them in the soil? I felt a little silly, splashing my bucket of water around the garden. Without a microscope, without any real scientific training, I was operating mostly on faith. I couldn’t see the nematodes, but I had to believe they were there, and I had to believe they’d find the cutworms somehow.
Because most nematodes are microscopic, it is easy to overlook their role in the soil. But Nathan Cobb, a pioneer in the science of nematodes, wrote, “If all the matter in the universe except nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.” It’s a creepy thought, all those invisible organisms covering us like a thin film. Even worse, one study reported about ninety thousand nematodes living in a single rotten apple. The soil is quite literally crawling with them: several thousand can be found in a half-cup of soil. The problem is that not all of them are good; some suppress plant diseases and others cause diseases.
Even though there are nematodes that can harm plants, their presence is generally considered a sign of good soil health. They are decomposers, feeding on bacteria and fungi, and sometimes parasitizing larger soil-dwelling creatures like the cutworms I was trying to get rid of. They’re also a major food source for earthworms, and certain species even rely on earthworms as a “reservoir host,” a vessel to shelter them during part of their life span. (I once saw a collection of tiny, barely visible nematodes, all gathered from the intestines of earthworms during dissection. About a dozen of them were in a vial together, and when they were held up to the light, looked like nothing more than dustlike particles drifting in a clear solution.)
Nematodes, along with the bacteria, fungi, and protozoa that inhabit the soil, are the unseen companions of the earthworm, serving as a food source, a collaborator, or—at times—a passenger in the earthworm’s gut, traveling distances and even finding a permanent home in the worm’s nutrient-rich intestine. This is the earthworm’s powerful secret, one that even Darwin didn’t fully grasp: the earthworm, far from being one of the smallest and weakest creatures, is actually one of the largest beings in its world, its underground society. In that place, it is an elephant, a whale—a giant.
SOIL BIOLOGISTS DESCRIBE what happens among the inhabitants of the soil in terms of a “food web,” as opposed to a “food chain,” for good reason: a chart of the complex relationships between earthworms and the other soil-dwelling insects resembles a spider’s web more than it does a hierarchical stepladder. The other inhabitants, apart from earthworms, are arthropods: insects such as mites, ants, spiders, millipedes, scorpions, beetles, sowbugs, and springtails. (Not all are visible to the naked eye: some, like certain mites and springtails, are microscopic.) These are often called “shredders” for their role in breaking down fallen leaves, bits of bark, and other organic matter. One soil scientist wrote that without arthropods, a bacterium in a pile of leaves would be like “a person in a pantry without a can-opener.” Like earthworms, arthropods break down the soil, build burrows through it, and add nutrients in the form of their castings. They outnumber earthworms by roughly four hundred to one: a square yard of garden soil might contain a few hundred earthworms, but it could contain one hundred thousand or more arthropods.
EARTHWORMS, THEN, ARE FAR from alone. Nowhere is this more evident than in my bin, where worms share space with a number of other creatures. I can’t say for certain how they got in the bin—because it sits outside, I suppose they just wandered in—but over time, I’ve found that they’re mostly harmless and may actually help worms do their jobs. So now I don’t mind having them around.
Pill bugs were one of the first creatures to crawl into the bin. Also called sow bugs, these are the little roly-poly crustaceans that carry hard grey armor on their backs and roll into a ball when provoked. They feed on decaying matter and are drawn to the damp conditions of the worm bin. They don’t harm the worms, and they’re not bad to have in the garden either, so I let them stay in the bin. When it’s time to harvest a tray of castings, I probably release a third of the sow bug population back into the garden, where they might, for all I know, make their way back to the worm bin eventually.
I also have a healthy population of pot worms. The proper name for them is enchytraeid worms; they are a distant cousin of earthworms and are sometimes mistaken for baby worms. But baby worms are faintly reddish and translucent; pot worms are solid white. They favor the same food source as earthworms, and their castings also become food for other microorganisms in the soil. I honestly don’t know how they made their way into the bin—I can’t imagine that they would come out of the soil and climb the plastic walls just to join the earthworms in their feast, but there they are. They work alongside the worms, often starting on food before the worms do. Perhaps they even help to break down the larger pieces of food—a chunk of cauliflower, a heel of stale bread—so the worms can go to work on it, too. That’s just my theory, but even if they don’t help, they certainly don’t hurt. I leave them alone, also.
For a while, I got so interested in the other inhabitants of the worm bin that I tried to add one into the mix. A local worm farmer showed me his bins, and I was surprised to see that the castings were covered in tiny white dots. It looked like someone had sprinkled salt or sugar on them, except that when I bent down to touch a few of the white spots, they jumped away. These were springtails, the same tiny white creatures that are sometimes found under a pile of leaves or at the base of a rotten log. They also feed on decaying plant matter, and they can be a vital part of a healthy soil community. I didn’t know why they had never appeared in my worm bin, but suddenly I wanted some. The farmer let me scoop out a shovelful of castings, which held more tiny springtails than I could count. At home, I added them to my own worms, but something in my bin must not favor the development of springtails, because when I went back and looked for them a few days later, I didn’t see any.
WHAT IS HAPPENING in my worm bin is really a microcosm of what’s going on in the soil. Add up the number of earthworms and other soil-dwelling creatures like mites, springtails, ants, and spiders, and there may well be more living things in one of my four-by-four vegetable beds than there are humans in all of rural Humboldt County where I live. Include the nematodes, and the population of one of those vegetable beds starts to rival that of the state of California. An earthworm could begin to feel a little crowded in such an environment. But it doesn’t end there: bacteria, fungi, and protozoa inhabit the soil—or the damp, dark confines of a worm bin—in far greater numbers. One teaspoon of soil could hold a billion bacteria, for example. It is here—at this microscopic level—that scientists are only just beginning to appreciate the critical role that earthworms play in the web of life that exists underground.
Picture a pinch of soil under a microscope. Large, irregularly shaped boulders—the clay and sand particles—stand surprisingly far apart from one another. The space between those particles makes up about half the volume of good, loose soil. In addition to allowing water and air to penetrate, the spaces give living organisms room to crawl around. Those creatures, along with the rotting organic matter they feed upon, account for only ten percent of the overall soil volume and show up under the microscope as tiny spots moving between the soil particles like black ants crawling around a rock. If an earthworm were to come across this scene, it could devour the whole community—soil particles, nematodes, bacteria, protozoa, and fungi—in one swallow.
To understand how earthworms interact with their microscopic counterparts, it is probably best to start with the single-celled bacteria that inhabit the soil by the billions. Bacteria help compost piles to decompose, creating the right environment for epigeic earthworms like Eisenia fetida. These worms won’t eat until bacteria have come in to start breaking down their food source. In fact, as long as the worms in my own bin have enough to eat, I’ve noticed that they will leave one of their favorite foods, a banana skin, alone for several days until it is more decomposed.
Some worm farmers recommend speeding up this process by inoculating new worm compost systems with bacteria-rich castings from another worm bin, or even by letting the food decompose in an ordinary compost pile before feeding it to them. If I had a much larger quantity of food to feed to my worms, I might do this myself. As it is, I’ve got only a handful of food scraps to give them each day; it is easier to scrape them right off the cutting board into the bin. They will decompose soon enough, and there’s always something else in the bin for the worms to eat that is farther along in the process.
Bacteria also contribute indirectly to the health of earthworms by helping plant life to flourish: some are responsible for converting ammonium into nitrate, a form of nitrogen that is easier for plants to use, others help fix nitrogen in the roots of plants, and still others help break down carbon, sulfur, hydrogen, and other compounds. In addition to transforming these nutrients into a form that is easier for plants to access, bacteria can help stabilize them, making them available in the soil for a longer period. A particular type of bacteria is even responsible for the fresh, earthy smell of soil. And although they are crucial to the health of soil and provide an abundant food source for earthworms, not all bacteria are beneficial. Some cause plant diseases. For example, the disease that causes squash and cucumber vines to wilt and collapse is caused by a particular soil bacteria.
What does it mean to a bacteria population, then, if earthworms are present in great numbers? One study showed over fifty different species of bacteria living in the gut of one nightcrawler. The intestinal mucus of a nightcrawler is an excellent food source for bacteria; they can thrive and reproduce inside the body of a worm, until far more bacteria emerge from the end of a worm than entered it in the first place. Still, an earthworm does not have an equally beneficial effect on every species of bacteria. Some are killed as they move through its intestinal tract, while others grow so rapidly that they can become the majority bacteria in a soil where they otherwise would have existed only in small quantities. Also, different species of earthworms may have unique relationships with certain bacteria. There’s been very little research done on this point, but when I asked oligochaetologists about it, all agreed that it was an interesting notion. “We don’t know for certain which species of earthworms might help a particular bacteria to flourish and to what extent,” one researcher told me. “But there are plant diseases that are caused by specific bacteria or fungi. If we found out that earthworms helped to spread those microorganisms, or helped to destroy them by encouraging their natural predator bacteria, that could be very useful information.”
IF BACTERIA CAN BE pictured as teeming black ants under the microscope, imagine fungi as gossamer spider webs. These organisms form long threads called hyphae that stretch between plant roots. Some form into even larger masses called mycelium that can span an entire backyard. Still others, called mycorrhizal fungi, cluster around plant roots and help bring nutrients and moisture to the root zone in exchange for the carbohydrates their host plant provides. Some farmers and gardeners who believe that these fragile, microscopic networks are too easily disrupted by deep ploughing, advocate churning the soil as little as possible. After all, fungi help decompose nutrients in the soil and keep them in place so that plants can use them.
But like bacteria, some fungi are harmful to plants. The verticillium wilt that plagues tomatoes each year is caused by a fungus, as are a variety of root rots that strike vegetable gardens. Once again, the best way to fight a fungus is with another one: the beneficial Gliocladium virens can prevent destructive fungi from getting established in soil. I have ordered it for my own garden in the last few years. Like the nematodes, this fungus comes in a surprisingly small package: one small foil pouch contains enough fungi, in the form of an ordinary-looking white powder, to inoculate most of my vegetable garden.
This spring my shipment arrived just in time; a week later and I would have been ready to put tomato plants in the ground. I tore open the package and walked through the vegetable garden, a shovel in one hand and the packet of beneficial fungi in the other. I stopped at each bed, turned the soil over, and sprinkled a little Gliocladium virens into the ground. It occurred to me that by distributing this fungus through my soil, I was changing the microscopic population of the earth. I was doing on a large scale what earthworms do on a small, but far more effective, scale.
There are all kinds of ways to tinker with the invisible life of the soil. Consider the way that researchers have used the earthworm in the fight against the take-all fungus Gaeumannomyces graminis. Take-all got its name from its ability to wipe out an entire field of wheat or barley in one season. The bacteria called Pseudomonas corrugata is effective against take-all, but researchers found that it was slow to move through the soil and attack the fungus. However, if it was mixed into sheep dung and then introduced to the soil, earthworms would eat the sheep dung and carry the bacteria through the soil, helping to move it more quickly to the roots of plants, where it could do its job.
Another wheat fungus, Rhizoctonia solani or bare-patch disease, decreases as the presence of particular earthworms increases, presumably because this fungus can’t survive the passage through a worm’s gut. But killing off a harmful fungus isn’t the only way earthworms can eliminate plant diseases: sometimes they help by carrying the fungus away from its host plant. One study showed that trees infected with apple scab benefited from large populations of nightcrawlers: the worms consumed the fallen leaves around the trees and carried the fungus on those leaves away with them in their guts, helping to disperse the colony of fungi that would have infected the tree anew in the spring.
What makes this situation so complex is that earthworms may help a particular fungus survive while killing off another one. Some of the most beneficial fungi—those most responsible for plant growth and nitrogen fixing—increase dramatically when they’re present, presumably because those fungi flourish in the nutrient-rich intestine of an earthworm. But other, harmful fungi have also been shown to thrive in the presence of earthworms. Dwarf bunt, a winter wheat disease, is one such fungus that can be spread by them. The dreaded tomato plant fungus, fusarium, might also be spread by an active worm population. Earthworms could have no particular effect on one harmful fungi, but might eliminate or help to spread that fungi’s main predator, thus tipping the scales in one direction or another. It seems unlikely that the risk of earthworms spreading diseases could ever outweigh their benefits. What we know for certain is that the earthworm is a powerful influence in the soil.
BACTERIA, FUNGI, AND nematodes are perhaps best known to gardeners like me because of the diseases they cause or combat. But from an earthworm’s perspective, protozoa may be the most important organisms in the soil. These multicelled creatures are quite a bit larger than bacteria, although still microscopic and still smaller, on average, than nematodes. Protozoa feed mostly on bacteria, competing with nematodes for this particular food source. A soil that is abundant in nematodes may have fewer protozoa, or vice versa, and even today scientists don’t know what this might mean to plant life. What is known for certain is that protozoa make up an important part of most earthworms’ diets. In fact, one study showed that Eisenia fetida could not reach sexual maturity unless protozoa were present in the soil. They thrive in compost piles, where they consume bacteria and, because bacteria contain more nitrogen than the protozoa need, they release excess nitrogen back to the soil. Like bacteria and fungi, many protozoa survive the trip through the earthworm’s gut and are found in large quantities in earthworm castings. Not all protozoa are equally nutritious to an earthworm: one scientist fed Eisenia fetida a restricted diet of two particular protozoa, and the worms died within a few days.
That brings up one of the great curiosities of earthworm life: in spite of all the microscopic creatures living alongside earthworms and inhabiting their guts, they seem to have few enemies in the soil. There have been a few stories of creatures that move into an earthworm’s body as a parasite and eventually destroy it: in Illinois, someone found a nightcrawler that was near death after a particular kind of nematode had taken it over. The nematodes caused a bacterial infection that killed the worm, then thousands of nematodes emerged from the dead worm’s body. (I saw a photograph of this event. I wish I hadn’t. The nematodes, at great magnification, themselves looked like tiny glistening white worms. They swarmed over their host, covering it so completely that I could not see the nightcrawler at all. It was a horrifying sight.)
But stories like this one are rare. More likely than not, a worm will not be harmed by the organisms passing through its gut and living alongside it in the dirt. Worms have more to fear from birds, moles, mice, and rats. They seem to suffer from very few parasitic or bacterial illnesses caused by the tiny creatures in their world. It is just another way in which worms seem to have a powerful ability to survive. An infection of streptococcus bacteria could, if left untreated, make me seriously ill. The sturdy constitution of the worm makes humans seem weak in comparison.
This once led me to call Sam James and ask him a silly question: how do worms die? If a worm manages to escape the robin’s beak, and if it is generally unmolested by parasites or other illnesses, what would kill it? And if they die of old age, what does that mean, exactly? In people, the symptoms of old age are obvious. A person might become frail and weak, their bones brittle, their skin fragile. One might die in old age of heart failure or cancer or a stroke. But what are the symptoms of old age in an earthworm? And why have I never found a dead worm in the soil, or, for that matter, in my compost bin?
Sam said that part of the reason I had never seen one is that they decompose so quickly. He told me that he once watched a dead worm in an underground root facility. “It lasted all of twenty-four hours before it totally vanished,” he said. “And I found a very nearly dead worm under a log once. Those are the only ones I have ever found in nature.”
As for how and why they might die of old age, he didn’t know, and I can only assume that if he doesn’t know, no one knows. There are no features that allow a person to tell a worm’s age, he explained. As long as it is an adult, a young worm looks the same as an old worm. Perhaps it makes sense that a creature that doesn’t get ill and has few enemies among its neighbors would also live agelessly and die without explanation or cause—would simply vanish without a trace.
WORMS PICK UP all kinds of odd organisms and objects as they eat their way through the dirt. They’ll swallow a tapeworm whole, for instance, and they can even consume a parasitic egg, burrowing deeper into the soil, where the egg is excreted in dark, safe surroundings that protect it from harm until it hatches. That makes farmers wonder if they could be a vector for transmission of parasites on the farm. And in the same way that worms can spread bacteria and other microorganisms, they have also been blamed for the spread of weed seed. A tiny, smooth, hard-shelled seed can pass quite safely through their guts. Researchers have observed worms choosing particular seeds over others and have suggested that in the right environment, they could act as powerful agents to spread the seeds of those plants they prefer.
Here’s an example of how intricate the relationships between worms and other microbes can be. A researcher once fed the bacterium Pseudomonas corrugata (which causes pith necrosis disease in tomatoes, but may also combat certain other plant diseases such as ring rot disease in potatoes) to four species of earthworms. One anecic worm, Aporrectodea longa, had ten times more Pseudomonas corrugata in its castings than did the other three worms in the study. If a farmer knew that Aporrectodea longa existed in the soil, he or she might be encouraged to know which worms could help spread bacteria that might prevent ring rot disease in potatoes. But if that farmer decided to plant tomatoes, those same worms spreading the same bacteria could put the tomato crop at risk for pith necrosis disease.
What’s a farmer supposed to do with this information? What could I do, in my own garden, to shift the subterranean population so that it favors the fruits and flowers I like to grow and keeps diseases and pests at bay? When I think about it like this, I realize that I have started to garden upside-down. I’ve begun to tend the soil the way I’d tend a farm, treating the bacteria, fungi, protozoa, and—of course—the earthworms, like a kind of livestock. When I add a shovelful of worm castings to the bottom of a planting hole where a new plant is about to go, I know that I am inoculating the earth with a concentrated population of invisible beings that I believe will shift the balance in the soil, creating a powerful community that will live at the feet of my new plant and perhaps even attract earthworms to the spot, where they will work to maintain and encourage the roots.
This is crude plant science, to be sure. But farmers and gardeners are increasingly turning to biological solutions for plant diseases and insect infestations, from ladybugs and parasitic wasps to nematodes and fungi. It does not seem so far-fetched, then, that farmers or gardeners could inoculate their soil with a particular earthworm that was known to do the most good—or, in the case of bacteria that cause plant diseases—the most harm. We know now that earthworms do more than plough the earth. They are at times the movers, incubators, or destroyers of the invisible denizens of the soil. But the study of earthworms is still in its infancy where soil microorganisms are concerned. It is far too early in the game for a scientist to recommend a particular earthworm as a biological solution to a farmer’s problem. Still, it is becoming clear that earthworms are, as one researcher put it, “a keystone species.” When an earthworm is introduced into a forest, a farm, or a backyard garden, it can bring about profound changes at the microscopic level, changes that can transform plant life aboveground.