. . . its history affords a striking exemplification of the divine truth, that no creature has been formed without its special ends, and that the humblest are frequently selected to carry out the most gigantic natural operations.
—JAMES SAMUELSON, Humble Creatures: The Earthworm and the Common Housefly, in Eight Letters, 1858
“WORMS HAVE PLAYED a more important part in the history of the world than most persons would at first suppose,” Darwin wrote in the conclusion of The Formation of Vegetable Mould. One biographer reports that his friend and colleague Joseph Hooker said this about Darwin’s book: “I must own I had always looked on worms as amongst the most helpless and unintelligent members of the creation; and am amazed to find that they have a domestic life and public duties!”
Those public duties extend far beyond the reaches of Darwin’s research. Even he might not have imagined that in the coming century, worms would be shown to have the ability to transform a forest, to destroy a rice terrace, and to accelerate the growth of greenhouse plants. He surely did not foresee the invention of a worm “reactor” that would harness the power of earthworms to consume tons of garbage. And he would have been astounded at the notion that anyone would try to make their fortune by raising earthworms for profit.
It is hard to predict where earthworm science will be at the end of the twenty-first century. But some tentative steps have been taken to solicit the assistance of earthworms in yet another human endeavor: the cleanup of pollution and the prevention of further damage to the environment. Since many pollutants eventually make their way into the soil, filtering down into the dark, damp places where earthworms live, this is, ironically, an issue as important to their future as it is to our own.
IT WAS NOT UNTIL the mid-sixties that a connection was made between earthworms and pollution. Worms had a talent that no one had paid much attention to before: they could take up pollutants in enormous quantities and live. Rachel Carson told the story in her groundbreaking book, Silent Spring.
Early studies showed that DDT (dichlorodiphenyltrichloroethane), an insecticide used to combat mosquitoes and lice, and thereby help fight malaria and typhus, would not gather in high enough concentrations in the soil or water to harm wildlife. This was proven wrong on several levels, and the practice of spraying DDT was stopped in this country thanks in large part to Carson’s book. Its use was widespread in the United States starting in about 1945; in fact, over a billion pounds of the pesticide was sprayed in this country during the thirty years it was in common use. By the early seventies, DDT was banned in the United States, although it is still used around the world, particularly in Africa, Asia, and Latin America.
It was Carson who reported that worms have an amazing ability to absorb whatever is in the soil, and they were able to take up huge concentrations of DDT into their tissue and still live. This was particularly a problem where elm trees were sprayed with DDT. The chemical remained on the leaves, not even washed off by rain, and in the fall, the trees dropped their leaves. Over the winter worms consumed the decomposing leaves, taking in large quantities of DDT. In the spring, the natural life cycle of worms and birds played itself out as usual: the worms came out of the ground at night; the birds foraged for stragglers early in the morning. But this time, the robins that ate worms also ingested what was stored in their tissue—a massive, concentrated dose of DDT.
Eating only eleven of these worms would be enough to kill a robin, and when you consider that a robin can eat ten to twelve worms in an hour, it’s no surprise that the worms were toxic enough to kill them. Some robins survived the high doses of poisoned earthworms, but were infertile and did not lay eggs the following spring. The lesson here is that earthworms were never factored into the analysis—such as it was—of the possible consequences of spraying DDT. Worms were simply overlooked, ignored, misunderstood—and their impact, their importance to the soil and to the ecosystem as a whole—was far greater than anyone could have guessed.
The fact that earthworms absorbed DDT in such high concentrations has not been lost on environmental scientists working in the areas of land reclamation and toxic clean-up. Perhaps the most significant achievement of earthworms yet will be their ability to help us out of some of the most awful messes we’ve created.
Earthworms have been used as biomonitors at toxic waste sites, where they quickly take up pollutants into their bodily tissue (they are particularly known for their ability to absorb metals like lead), often surviving long enough to be collected by monitors and tested. In this way, worms become the canary in the coal mine, giving a clear picture of the extent to which chemicals present in the soil or groundwater are affecting soil organisms and, by extension, other animals living at the site. Over the years, protocols have been developed for introducing earthworm species into contaminated areas and testing them for exposure to pollution. The EPA, the U.S. Army Corps of Engineers, and other agencies have developed programs using earthworms as biomonitors. These tests, called “bioassays,” are particularly important for monitoring the many potential pollutants for which there are no other conventional measurements. By tracking the levels of toxins in earthworm tissue, scientists can now monitor pollution issues that were previously difficult to quantify, such as the cumulative effect of pollutants over time and the impact of several toxins in combination.
Some of the most exciting new work with earthworms goes beyond using them simply to monitor pollution. Scientists are now exploring ways in which they can be used to break down toxins and actually clean up pollution. Dr. Andrew Singer at Oxford University recently investigated the use of worms to clean up soil contaminated by polychlorinated biphenyl (PCB). PCBs are mixtures of synthetic organic chemicals used in electrical equipment, paints, rubbers, dyes, plastics, and many other industrial applications. The EPA banned manufacture of PCBs in the United States in 1979 and has been overseeing a gradual phase-out of their use in existing equipment, as well as clean-up of sites contaminated by PCBs, since then.
“As it turns out, PCBs were first detected in bird extracts when scientists were looking for DDT,” Singer told me. “They didn’t know what the PCBs were at first. They just thought they were some weird anomalies—this is back in the mid-1960s—then a researcher just got lucky and figured out that the anomalous chemicals that were being extracted from birds all over the place were in fact PCBs, and thus the explosion of interest in PCBs in the early 1970s. Somewhat similar to the DDT story.”
PCBs have been described by the EPA as “extraordinarily toxic.” It has been estimated that there are over one billion pounds of PCB compounds in the environment. They can accumulate in fatty tissue and have shown up in the breast milk of Inuit women in northern Quebec. Although PCBs have been identified as possible carcinogens, their worst effects seem to be related to the nervous system and brain functions. Birds who have high accumulations of PCBs in their tissue end up with odd genetic defects and are sometimes unable to build a proper nest. They are dangerous, persistent toxins that do not easily break down.
Singer knew that some work had been done on the use of bacteria to break down PCB in the soil. However, it was proving difficult to get the microorganisms completely incorporated into the dirt without actually excavating the area and mixing it in manually. Also, the bacteria rely on oxygen to survive, and in some compacted, polluted soils there was simply not enough oxygen available for the organisms to live. Singer was surprised to learn that, in spite of the widespread knowledge of earthworms’ ability to aerate the soil and transport microorganisms, few people had given any thought to using worms to incorporate specific bacteria into the soil for a clean-up project.
For his experiments, Singer chose an anecic worm—not Lumbricus terrestris, but Pheretima hawayana, a large fishing worm sometimes called a tropical nightcrawler that has also gone by the nickname California Golden and Alabama Jumper. This is a deep-burrowing worm that Singer knew would move constantly between the soil surface and the deep underground layers, bringing dirt up in the form of castings, where it could be repeatedly inoculated with the bacteria. He was also able to test the soil where the earthworms had been introduced to show that they were increasing the oxygen level belowground. In each of his experiments, more PCBs broke down when earthworms were present. The degradation of PCBs was also much more consistent throughout the entire soil area thanks to the earthworms. Finally—and this is perhaps the most extraordinary outcome of his research—he found that PCBs broke down faster when earthworms were present, even if no PCB-degrading bacteria had been introduced into the soil. He assumed that this was due to the fact that earthworms create a soil environment that is naturally more rich in microorganisms of all kinds, and that those microorganisms might have helped to break down the pollutant.
Singer used a fairly high concentration of earthworms for his experiments. It’s not always so easy to get a worm population established in the wild, which is one of the major challenges scientists face when they’re trying to use earthworms to carry out certain jobs. Right now, PCB-contaminated soil is most often excavated when it is discovered, and stored in large containers. Eventually, they would be taken to a landfill or burned. These soil-filled drums, Singer pointed out, are perfect for introducing large populations of earthworms. The environment can be controlled so that the conditions are just right for the earthworms to thrive, and scientists can expect fairly consistent results from each container.
There was one more conclusion to Singer’s research, not much more than a footnote, but it points out the new directions in which earthworm science may be headed. While he was measuring the soil to see how much the earthworms increased oxygen levels belowground, he made an unexpected discovery. Soil that had a large earthworm population seemed to break down methane at a higher rate than soil without earthworms. Because methane is one of the most common greenhouse gases, it is widely believed to be a major contributor to global climate change. It is no secret that organisms in the soil can transform methane: peat bogs have a unique ability to consume methane and carbon dioxide from the atmosphere. They also give off methane, and some scientists speculate that there is a fragile balance between the organisms that emit methane and those that consume it in bogs. In the same way, earthworms help create soil conditions in which this balance exists. All Singer can say at the moment is that the notion of earthworms helping to reduce greenhouse gas is worth looking into. When he published his findings, he wrote, “The proposed effect of earthworms on enhanced methane consumption has relevance to global environmental change and is the subject of further study in our laboratory.”
IF ANDREW SINGER is cautious about the potential for earthworms to clean up pollution and reduce greenhouse gases, he has every right to be. Earthworms are living creatures, fragile and temperamental, and experiments using them do not always turn out the way researchers expect. Over the last few decades, scientists have looked into the possibility of using earthworms to reclaim abandoned strip mines and rock quarries, where a chunk of earth, sometimes half a mountain, has been hauled away, leaving a hole that looks like an open wound. The idea was that earthworms could come in and close the wound, stabilizing the soil, working leaf litter into the ground, and making it possible for plants to get established. Depending on the conditions at the site—often the topsoil has been removed, exposing a layer of subsoil that simply won’t support plant life—it can take years for a substantial earthworm population to build up on its own, but by using the techniques already made popular by organic farmers—minimal tillage, cover crops, the addition of compost and manure—worm populations could build up quickly and, in turn, help bring about natural restoration of the land.
Bringing worms into these kinds of damaged sites presents the same problem that farmers face if they want to introduce worms to their soil: it is not easy to find the right worm in sufficient quantities. Also, the soil might be too acidic for most species of earthworms. Finally, introducing earthworms into a climate that is either too hot or too cold will be self-defeating. It’s a slow process. Even when earthworms have been brought into abandoned strip mines and rock quarries, it has taken up to ten years for them to fully establish themselves.
I talked to Jack Vimmerstedt, an expert in strip-mine reclamation at Ohio State University. He published several papers over the last few decades about the potential for using earthworms in these damaged areas. Ohio coal-mining laws required land to be restored after the mining was complete, and Vimmerstedt speculated that earthworms such as Lumbricus terrestris could be used to help build up sugar maple forests after strip mining. “I figured they’d bury the leaf litter, bring new soil up to the surface, and just help to build up the earth,” he told me. “And they did. Sugar maple, European alder . . . those leaves are like ice cream and candy to worms. They ate it up. Except . . .”
I was already thinking about the exotic worms in Minnesota’s forests. “Except the forests in Ohio probably didn’t have nightcrawlers to begin with, right?”
“Well, that’s right,” he said. “Lumbricus terrestris has gotten a bad name for itself when it comes to forests. It’s been tagged as an invasive species. So maybe it’s not such a good idea to fill a forest with nightcrawlers. Besides, now the state would rather see strip mines turned into pasture instead of forest.”
“Worms are supposed to do great in pasture, aren’t they?” I asked.
“Sure,” he said. “We tried introducing worms to help get new pastures established, but when we went back two years later to check on them, we couldn’t find any. Why? Well, one reason might have to do with the fact that they stockpile the topsoil and bring it back to the site after the strip mining’s done. Some of the spoil material is rich in pyrite, and it’s just too acidic for the worms. That could be one of the problems. Besides, it’s just hard to tell what worms might do in a new environment.”
Eventually, he reached the conclusion that there might not be a role for worms to play in the reclamation of strip mines. But that’s only because he was looking at the short term, thinking in increments of ten years instead of a million years. In the long run, earthworms can reclaim strip mines, along with everything else. They will continue their slow, incremental work, consuming earth, bringing castings to the surface, and creating, over time, a new landscape.
SOMETIMES I WONDER if it is too much of an imposition on earthworms to push them into polluted ground, or to force-feed them a particular bacteria because we’d like to see it spread around. Darwin noticed that humans tend to exploit any characteristic for their own good, writing that “in the process of selection man almost invariably wishes to go to an extreme point.” Are we taking advantage of earthworms? Shouldn’t we clean up our own messes, or learn not to make them in the first place?
Earthworms are the custodians of the planet. They were here for millions of years before we came along. They survived the extinction that killed off the dinosaurs; I imagine they’d do just fine if something came along and wiped us out, too. Eisenia fetida may have grown particularly accustomed to food supplied by humans, but most of the species of worms around the world have little contact with us.
Darwin realized that earthworms, collectively, were a force to be reckoned with. Whether or not it is ethical or wise for us to enlist their help in fertilizing our farms, or cleaning up our pollution and garbage, we should remember one thing: we need worms more than they need us.